BACKGROUND: Trichotillomania, a disorder of hair pulling, has been considered a rare condition. Estimations of the prevalence of this disorder have been based largely on clinical experience, and there have been no estimates of its prevalence based on data collected from a large, nonclinical population. METHOD: 2579 freshman college students at two state universities and one liberal arts college were asked to provide written responses to questions designed to practically apply DSM-III-R criteria for trichotillomania and estimate the prevalence of trichotillomania in this population. RESULTS: 2534 students (97.9% of the study population) responded. We found a 0.6% lifetime prevalence of DSM-III-R trichotillomania for both male and female respondents. Hair pulling resulting in visible hair loss, but failing to meet full DSM-III-R criteria, was identified in 1.5% of males and 3.4% of females. CONCLUSION: Trichotillomania may not be as rare as previously suspected and may affect males as often as females.