Objective: The study objective was to determine whether medical students' attendance at a rehabilitation residence for pregnant women with substance-use disorders yielded changes in their attitudes and comfort levels in providing care to this population. Methods: This randomized educational trial involved 96 consecutive medical students during their obstetrics and gynecology clerkship. In addition to attending a half-day prenatal clinic designed for women with substance-use disorders, every student was randomly assigned either to attend (Study group) or not to attend (Control group) a rehabilitation residence for pregnant women with substance-use disorders. The primary objective was to measure differences in responses to a confidential 12-question survey addressing comfort levels and attitudes, at the beginning and end of the clerkship. Results: Survey responses revealed improvements in students' comfort levels and attitudes toward pregnant women with substance-use disorders by attending the clinic alone or the clinic and residence. Those who attended the residence reported becoming more comfortable in talking with patients about adverse effects from substance abuse, more understanding of "street" terms, and stronger belief that patients will disclose their substance use to providers. Residents expressed more openly their hardships and barriers while trying to set therapeutic goals. Conclusions: Medical students became more comfortable and insightful about pregnant women with substance-use disorders after attending a rehabilitation residence in addition to a prenatal clinic dedicated to this population.