Physicians' religious attributes are unknown, and may affect patient care. The Women Physicians' Health Study (WPHS) is a random sample (n = 4501 respondents, 59% response rate) of US women physicians aged 30-70; the first large, national study of US women physicians. In this study US women physicians were less likely to be Christian than were other Americans (61.2% of women physicians versus 85.1% of the general population), but were more likely to be Jewish (13.2% vs 2.0%), Buddhist (1.4% vs 0.3%), Hindu (3.9% vs 0.4%), or atheist/agnostic (5.9% vs 0.6%). Protestantism (29.3% of the population) and Catholicism (24.9%) were the most commonly reported religious identities. The strongest religious identity was claimed by Mormons and Seventh Day Adventists. Thus, women physicians' religious beliefs differ from those of the general population in the US. This may be particularly important for physicians practicing with patient populations with different religious affiliations, and in addressing clinical questions with ethical or religious dimensions.