Getting sick sure works for David Letterman.

His return to the "Late Show," after being waylaid for a month by a case of shingles, helped him earn his second-highest ratings this season and his biggest victory over NBC late-night rival Jay Leno in three years, reports Reuters.

According to preliminary Nielsen Media Research figures, Monday's Letterman show earned a 5.3 rating, its highest rating since self-help guru Dr. Phil McGraw joked with Dave on Feb. 17 -- and allowed Letterman to better Leno's "Tonight" show in overall ratings for this season.

Monday marked the second time this season that Letterman beat Leno in overall ratings. It also was the steepest percentage gain (23 percent) over Leno since Letterman's return to his desk in February 2000 following his open-heart surgery.

"Thirty days it took me to get over the shingles, and according to Donald Rumsfeld, that's right on schedule," Letterman, 55, said on Monday's show, after his shoes had been filled by 14 substitute guest hosts and reruns during his absence.

Shingles is a viral infection related to chickenpox and is known for being highly painful. "It hurt so much I was Michael Jackson-crazy," said Letterman.

He also paid tribute on Monday's show to his dermatologist, Richard Granstein of Manhattan, who was presented with a bouquet of flowers by two nurses -- actually models named Nadine and Andrea.