To determine the attitudes of obstetricians and gynecologists toward hormone replacement therapy (HRT), and the beliefs and intuitions that affected those attitudes. A questionnaire was sent to 1,000 gynecologists in the United States; 328 replies were received. The questionnaire asked about effects of HRT, practices concerning HRT, and decisions in hypothetical scenarios. The respondents strongly favored HRT, and they were well informed about its effects on osteoporosis, cardiovascular disease, and breast cancer. They were aware of conflicting findings concerning breast cancer. The strength of their recommendation of HRT was sensitive to patient differences in risk factors. The respondents also showed four biases hypothesized to cause resistance to HRT: omission bias (more concern about harmful acts than harmful omissions); proportionality bias (attention to relative risk rather than risk differences); naturalness bias (preference for the natural); and ambiguity (avoiding options with missing information). Proportion bias, naturalness bias, and (weakly) omission bias were related to less favorable attitudes toward HRT. Although specialists are highly favorable toward HRT in general, some negativity toward HRT may result from decision biases.