Hospital policies and culture aff ect abortion provision. The prevalence and nature of colleague opposition to abortion and how this opposition limits abortion care in U.S. teaching hospitals have not been investigated. METHODS : As part of a mixed-methods study, a nationwide survey of residency and site directors at 169 accredited obstetrics-gynecology training programs was conducted in 2015-2016, and 18 in-depth interviews with program directors were conducted in 2014 and 2017. The prevalence and nature of interprofessional opposition were examined using descriptive statistics, and regional diff erences were investigated using logistic regression. A modifi ed grounded theoretical approach was used to analyze interview data. RESULTS : Among the 91% of survey respondents who reported that they or their colleagues had wanted or needed to provide abortions in the prior year, 69% faced opposition from colleagues. Most commonly, opposition came from nurses (58%), nursing administration (30%) and anesthesiologists (30%), manifesting as resistance to participating in or cooperating with procedures (51% and 38%, respectively). Fifty-nine percent of respondents had denied care to patients in the prior year because of colleagues' opposition. Respondents in the Midwest and South were more likely than those in the Northeast to deny abortion care to patients because of such opposition (odds ratios, 3.2 and 4.4, respectively). Interviews revealed how participants had to circumvent opposing colleagues, making abortion provision diffi cult and leading to delays in and, infrequently, denial of abortion care. CONCLUSIONS : Interprofessional opposition to abortion is widespread in U.S. teaching hospitals. Interventions are needed that prioritize patients' needs while recognizing the challenges hospital colleagues face in their abortion participation decisions.