Baila Steinman first noticed the numbness in her leg on a trip to Israel in December. "From the knee to the pelvis, it was numb to the point of being painful," recalls the 52-year-old occupational therapist.

Back home in Brooklyn, a neurologist had her balance on her toes, walk backward on her heels and push back when he put pressure on her legs. Then he asked, "Do you wear tight clothes? Control-top pantyhose? Tight belts?" When she nodded yes, the doctor, Irving Friedman, exclaimed "That's it!"

The culprit: the cinch belts Mrs. Steinman loves to wear. Dr. Friedman said they can compress a major nerve, the lateral, femoral cutaneous nerve, that runs from the abdomen to the outer thigh. He said he frequently sees the condition—called meralgia paresthetica—in policemen who carry guns on their hips and ballet dancers who wear tight tutus. "Anything that puts pressure on that nerve can cause it," he said. "It's very, very common."

Mrs. Steinman still wears the belts she loves, just not buckled quite so tight. "I told my friends about this and they cracked up," she says. "I said, 'I'm just letting you girls know, this can happen to you.' "