As a leading cause of hysterectomy in premenopausal women. uterine leiomyomas are a major public health problem. However, very little work has been done on their epidemiology. Indeed, their true frequency has never been established using systematic and meticulous methods. In this study, gross serial sectioning at 2-mm intervals was applied as an adjunct to routine pathology processing in 100 consecutive total hysterectomy specimens. This tripled the number of leiomyomas noted in routine pathology reports. There were 649 leiomyomas in 77 of 100 uteri, with multiplicity of leiomyomas in 84%. Although leiomyomas were more numerous and larger in women with a clinical diagnosis of myomatous uterus, the incidence was no higher than in uteri removed for other reasons. The postmenopausal incidence of leiomyomas was no lower than the premenopausal incidence, although postmenopausal leiomyomas were smaller and fewer. These findings suggest that epidemiologic studies of leiomyomas may not be valid if they are based only on clinical diagnoses or routine pathology reports.