The characteristics that differentiate long-term (> or = 10 years) hormone replacement therapy (HRT) users from short-term (<10 years) users and nonusers are not well documented. The epidemiology of long-term HRT use was investigated within a random sample survey of 703 women aged 50-80 years who were members of Group Health Cooperative (GHC) of Puget Sound. Women who had been menopausal for > or = 10 years comprised the study population. Long-term HRT users (29.4 percent) were compared with short-term (28.1 percent) and never users (42.5 percent). The authors examined the association between duration of HRT use and demographic characteristics, personal and family medical history, menopausal symptoms, information used in decision making, attitudes toward HRT, provider encouragement to use HRT, and GHC utilization. Compared with never users, the strongest correlates of long-term HRT use were having a hysterectomy before or after menopause, positive attitudes espousing the benefits of HRTs, and perceived provider encouragement to use HRT. Long-term HRT use was not associated with educational attainment, ethnicity, body mass index, health status, physical activity, or family medical history. Correlates commonly associated with HRT use, such as higher education, greater physical activity and functioning, and lower chronic disease comorbidity, did not significantly distinguish long-term from short-term users.