OBJECTIVE: To characterize the prevalence of objections to assisted reproductive technologies among obstetrician-gynecologists. METHODS: We conducted a national probability sample mail survey of 1,800 practicing U.S. ob-gyns. Criterion variables were whether physicians object to artificial insemination or in vitro fertilization. We also presented seven patient scenarios and asked respondents if they would discourage use of assisted reproductive technologies and if they would help patients access such technologies. Covariates included physician demographic and religious characteristics. RESULTS: : Of 1,760 eligible ob-gyns, 1,154 responded (66%). Few (less than 5%) object to artificial insemination or in vitro fertilization, and even fewer (less than 3%) would not help patients access these technologies. However, the majority of ob-gyns would discourage using assisted reproductive technologies if pregnancy has a 25% mortality risk (95%), if the patient is 56 years old (88%), or if the patient has human immunodeficiency virus (73%). Fewer would discourage use of assisted reproductive technologies if the patient already has five healthy biological children (24%), if she plans to be a single parent (17%), if she is not married to her male sexual partner (14%), or if her sexual partner is female (14%). Male (odds ratio, 2.2-2.8) and religious physicians (3.6-4.7) were more likely to discourage using assisted reproductive technologies if the patient was lesbian, single, or unmarried. CONCLUSION: Few ob-gyns object to assisted reproductive technologies. Most discourage use of such technologies for patients with advanced age or medical comorbidities. Male and religious physicians are more likely to limit access for lesbian, single, or unmarried patients. LEVEL OF EVIDENCE: III.