OBJECTIVE: Previous research has found that physicians are divided on whether they are obligated to provide a treatment to which they object and whether they should refer patients in such cases. The present study compares several possible scenarios in which a physician objects to a treatment that a patient requests, in order to better characterise physicians' beliefs about what responses are appropriate. DESIGN: We surveyed a nationally representative sample of 1504 US primary care physicians using an experimentally manipulated vignette in which a patient requests a clinical intervention to which the patient's physician objects. We used multivariate logistic regression models to determine how vignette and respondent characteristics affected respondent's judgements. RESULTS: Among eligible respondents, the response rate was 63% (896/1427). When faced with an objection to providing treatment, referring the patient was the action judged most appropriate (57% indicated it was appropriate), while few physicians thought it appropriate to provide treatment despite one's objection (15%). The most religious physicians were more likely than the least religious physicians to support refusing to accommodate the patient's request (38% vs 22%, OR=1.75; 95% CI 1.06 to 2.86). CONCLUSIONS: This study indicates that US physicians believe it is inappropriate to provide an intervention that violates one's personal or professional standards. Referring seems to be physicians' preferred way of responding to requests for interventions to which physicians object.