Dr. Ruth Westheimer, the relentlessly cheerful First Lady of Sex, is rightly esteemed for the solid information she imparts on her phone-in radio and TV shows. But alas, even Dr. Ruth can make a boo-boo—and this one is a lulu.

In her latest book, First Love: A Young People's Guide to Sexual Information, the expert advises women that it is safe to have intercourse during the week before and the week of ovulation. She couldn't have been more wrong, since that is precisely the time when women are most likely to get pregnant. "It's very upsetting," admits Dr. Ruth. "I don't know how many times I read over that passage, but I just must not have been attentive enough."

First Love, which followed Dr. Ruth's Guide to Good Sex, was in bookstores for three months before the goof was discovered. Ann Scarpellino, 51, who screens books for children and young adults at the Free Public Library in Ramsey, N.J., flipped when she read the chapter on contraception. "I couldn't believe it," says Scarpellino, the mother of three children. "Anyone who has given birth knows the week before and the week of ovulation are the times when you are most fertile."

Fearing that teenage readers might not be so well-informed, Scarpellino immediately called the publisher. Warner Books hurriedly recalled the 115,000 copies already in distribution and hoped to have a corrected version of the $3.50 paperback available by the end of January. Westheimer also issued a warning immediately on her nationally syndicated radio talk show Sexually Speaking and on her Lifetime cable series The Dr. Ruth Show.

Scarpellino applauds Dr. Ruth for openly acknowledging her error and says she will place a revised copy of First Love on her library shelves. Some of Scarpellino's professional colleagues, however, are more cautious. "[Some] medical information, such as why the sponge is risky and how the Pill works, is simplified into obscurity," writes a School Library Journal critic. "For many teenagers, [First Love] will raise more questions and create more confusion than it will answer."

Teenagers wishing to avoid more than just confusion can turn in their early copies of First Love for a free replacement. The corrected edition has a new cover. "The book first came out in white," says Dr. Ruth. "But I made a mistake, I blushed, now it's red."