OBJECTIVE To test the effectiveness of a brief intervention in the reduction of prenatal alcohol consumption by women when a partner is included. METHODS Randomized trial of a single session brief intervention given by the study nurse or principal investigator for 304 pregnant women and their partners. The women had positive T-ACE (Tolerance, Annoyed, Cut down, Eye-opener, an alcohol screening test) results and were at risk for alcohol consumption while pregnant. All completed initial diagnostic and postpartum interviews. RESULTS Fewer than 20% of participants (median 11.5 weeks of gestation) were abstinent at study enrollment, averaging more than 1.5 drinks per episode. Nearly 30% had 2 or more drinks at a time while pregnant. Prenatal alcohol use declined in both the treatment and control groups after study enrollment, based on a 95% follow-up rate. Factors associated with increased prenatal alcohol use after randomization included more years of education, extent of previous alcohol consumption, and temptation to drink in social situations. Brief interventions for prenatal alcohol reduced subsequent consumption most significantly for the women with the highest consumption initially (regression coefficient, b = -0.163, standard error (b) = 0.063, P < .01). Moreover, the effects of the brief intervention were significantly enhanced when a partner participated (b = -0.932, standard error (b) = 0.468), P < .05). CONCLUSIONS Pregnant women with the highest levels of alcohol use reduced their drinking most after a brief intervention that included their partners. Recommendations include consistent screening for prenatal alcohol use followed by diagnostic assessment when indicated, and if confirmed by other studies, a patient-partner brief intervention for the heaviest drinkers.