Women with mammary hypertrophy who present for reduction mammaplasty have several well-described musculoskeletal complaints, but a high prevalence of carpal tunnel syndrome has not been reported. We identified 151 patients from a plastic surgery practice who underwent reduction mammaplasty from 1994 to 1996. To this group we added a convenience sample of 64 women volunteers with relatively smaller breasts (brassiere cup size B or smaller). We questioned the entire group about specific symptoms and examined them using standard provocative tests. Carpal tunnel syndrome was defined as the coexistence of symptoms and at least two physical examination findings. We examined its association with breast size, age, race, and body mass index. Stepwise logistic regression was used to determine which physical characteristics were predictive of the condition. Carpal tunnel syndrome was found in 30 patients (19.9 percent) (95 percent confidence interval, 13.8 to 27.1) and in none of the women in the convenience sample. Breast size and, to a lesser degree, body mass index were found to be highly significant predictors of carpal tunnel syndrome. After controlling for breast size, race was also significant. Breast size displayed an independent risk ratio of 6.67 when comparing the upper quartile of size to the lower quartiles. There is a markedly higher prevalence of carpal tunnel syndrome in women who present for reduction mammaplasty than in those with smaller breasts. Breast size was a significant predictor of carpal tunnel syndrome.