One day a teacher had a simple request for Toby Scheib: Would he hand out some papers she had graded to the class? The only problem was that the middle schooler had a secret. He suffered from an inherited condition called face blindness, which made it all but impossible for him to recognize any of the kids in the class, even those he had been in school with for years. If nothing else, being face blind has made Toby, now 14, highly resourceful. "I kind of panicked," he recalls. "Then I thought of a simple solution. I asked the kids to come up and get the papers when I called their names."

It is something nearly everyone takes for granted—the ability to recognize family, friends, neighbors and coworkers. But for those suffering from face blindness—which is formally known as prosopagnosia—the routine act of greeting others can be fraught with anxiety. It is not that they can't see people. Their eyesight is fine. But because of an impairment in the brain, they are unable to remember what people look like. "If I look at someone and close my eyes," says Toby's mother, Elaine, who also suffers from face blindness, "when I look back, it's like I'm seeing them for the first time."

As strange as that seems, it may not be all that rare. At least 10 members of Toby's extended family—including his mom and father Bill, who live in Las Vegas—have been diagnosed with the incurable disorder. (It can also be acquired through stroke and some brain injuries.) Researchers estimate that as many as one in 50 people could suffer from some degree of face blindness (see box), often without letting on even to family members and close friends. "These people get around it by hook or by crook," says Prof. Ken Nakayama of Harvard University, who is studying prosopagnosics, including the Scheib family. "I'm shocked sometimes at how well some people are able to function."

Still, for those with face blindness the everyday obstacles are daunting. Elaine, 50, a stay-at-home mom, says she could not recognize her own children—Toby and her daughter, Kelcey, 17—until they were about 4 years old and she could identify them through constant repetition of their facial characteristics. (Usually people with face blindness rely on such factors as voice, hair and context to try to identify someone.) Elaine's concern over not being able to tell one child from another, or one teacher from another, was so great that she never enrolled them in preschool. "It was scary," she says. "It would have been like dropping them off with strangers every day." Despite her care, she once lost Toby at an Easter egg hunt when he was 7. Frantic, she found a police officer but couldn't do much more than tell him what her son was wearing. "How do you describe what your own child looks like when you don't know?" says Elaine. "Without him in front of me it was really hard." These days she is able to pick out her kids and husband but hardly anyone else.

For instance, she has seen the nextdoor neighbors on many occasions over the past three years, but she's helpless to recognize them. "If someone's working in their yard," she says, "I don't know if it's the owner or the gardeners." As husband Bill, 60, points out, face blindness can drain much of the pleasure out of even watching a movie. "When you have a complicated plot, we get totally lost," he says. "All the actors look like Tom Cruise."

Though Toby is bright and personable, his face blindness has left him socially isolated. "I have to identify people by how they walk and carry themselves," he says—though when he playfully holds up his three pet ferrets he has no trouble telling them apart. He has almost no playdates and sits alone on the bus to school in the morning. He doesn't tell many people about his condition, mainly because he is met with disbelief when he does. "It kind of blows over their heads," says Bill. "They don't have a clue what he's talking about." Last year he did have a girlfriend for a while, though the relationship had its difficulties—starting with the fact that he couldn't remember what she looked like. Sister Kelcey, who is not face blind, recalls a time when Toby was supposed to meet up with the girl at a fair but insisted that Kelcey come along to pick her out. "He didn't want to leave my side," she says, "because he thought he wouldn't see her."

Courtship can be difficult for any couple, but for Elaine and Bill—a retired Air Force meteorologist who now works as a poker dealer at the Boulder Station casino in Las Vegas—it was particularly dicey. "It's amazing to me that we even managed to come together," says Elaine. Trying to recognize Bill from any distance in his uniform, especially if there were other Air Force personnel around, was next to impossible. The only saving grace were the little name tags that the airmen wore, which she would discreetly and hurriedly scan when meeting up with him. If they happened to get together and he was in his civvies, there could be some anxious moments. "Even when I was up close I wasn't always certain I was talking to him," she says. "There were a few times when I was sweating bullets." They never told one another about their shared difficulties with faces, and it took a year of dating before Elaine could begin to recognize her future husband. "By the time we got married I could pick him out of a crowd," she says proudly.

It is the sort of bizarre predicament that bonds face-blind people together. Heather Sellers, 43, an English professor at Hope College in Michigan who has a severe case of prosopagnosia, has trouble even recognizing herself. "I'd go to a friend's house to watch home videos, but I'd never see myself," she says. "It's chilling and weird because I know I'm there." She also recalls the time she looked out in the backyard and didn't recognize the man standing there in a pair of bib overalls. "I thought it was a utility worker," she says. "It turned out to be my then-husband. I'd just never seen him in that suit." Indeed, as Harvard's Nakayama points out, romance is often the factor that convinces the face blind that they have a problem. "A lot of people don't realize it until they go to college," he says, "and they come out of the bathroom and wonder, 'My God, where's my date?'"

But how could someone not know early on that he or she was deficient in such a crucial area of life? Quite easily, to hear face-blind people tell it. Bill long realized that he had trouble with faces that others didn't seem to have. But he convinced himself that the issue was psychological rather than physical. "I just felt I was lacking in some social skill," he says, "that I wasn't trying hard enough." Elaine also kept silent growing up, never mentioning her condition to her parents, or even her five brothers and sisters—four of whom also had face blindness but likewise kept mum. It wasn't until she was 40 that she broached the subject with sister Kate, who began researching the problem. From there the secret the siblings had kept from each other began to come out.

Elaine and Bill believe that stress over his face blindness is what led Toby to plunge into a depression a year and a half ago. This year he is doing much better, especially in school, where his parents have made a point of enlisting the help of the staff to ease his way. Now when teachers approach Toby in the hall, for instance, they give him a verbal cue of who they are. And if nothing else, just knowing there is a physical basis for his difficulty has been reassuring. "Before, I thought I just had a bad memory," he says. "Now I have enough skills to get around it."