OBJECTIVETo estimate the incidence and regression rates of uterine leiomyomata and polyps in a cohort of asymptomatic, premenopausal women.METHODSSaline infusion sonography was performed twice, 2.5 years apart, in a cohort of 64 initially asymptomatic women. Subjects completed a questionnaire that assessed the development of abnormal uterine bleeding.RESULTSThe mean age of women (at second ultrasound) was 44 years. In four of seven women with polyps at the original ultrasound, their polyps regressed. Polyps that regressed tended to be smaller than polyps that persisted. Ten women had endometrial polyps at the second ultrasound for a point prevalence of 16% and a cumulative incidence rate of 12% per 2.5 years. A higher percentage of women with uterine polyps had complaints of abnormal uterine bleeding than women with no uterine abnormalities (70% versus 33%,P= .04). Six leiomyomata in four women were no longer detected in the second ultrasound. Leiomyomata that regressed were in older premenopausal women and were smaller than leiomyomata that persisted. The point prevalence and incidence rates of leiomyomata were 27% and 13% per 2.5 years, respectively. Leiomyomata grew an average of 1.2 cm per 2.5 years, but great variation in growth rates were noted.CONCLUSIONSmall uterine polyps frequently regressed spontaneously, whereas larger polyps were more likely to persist and were associated with the development of abnormal bleeding. Smaller leiomyomata in older premenopausal women also regressed whereas larger leiomyomata tended to grow while often remaining asymptomatic.