Objective: This randomized controlled trial tested the efficacy of motivational interviewing (MI) to reduce alcohol use among heavy drinking men who have sex with men (MSM) who are engaged in HIV care but not currently receiving addictions treatment. Method: One hundred eighty MSM living with HIV—recruited regardless of interest in changing drinking—were randomly assigned to MI or an assessment-only treatment as usual (TAU) control. MI comprised one in-person session followed by two brief phone calls and in-person booster sessions at 3 and 6 months. The Timeline Follow-Back Interview assessed past 30-day alcohol use and sexual behavior at 3, 6, and 12 months postbaseline, and serum samples and medical records assessed viral load, CD4 cell count, and liver function. Results: At 6 and 12 months, MI compared to TAU resulted in significantly fewer drinks per week (6 months: b = −8.72, 95% confidence interval (CI) [−12.69, −4.76]; 12 months: b = −5.98, 95% CI [−9.77, −2.19]) and lower number of heavy drinking days (6 months: incidence rate ratio = 0.55, 95% CI [0.38, 0.79]; 12 months: incidence rate ratio = 0.50, 95% CI [0.33, 0.78]). Effects on viral load, CD4 cell count, and liver function were nonsignificant. Among those reporting condomless sex with nonsteady partners at baseline, MI resulted in significantly lower rates of this behavior at 3 and 12 months compared to TAU. Conclusions: In MSM living with HIV, MI shows substantial promise for reducing heavy drinking and for reducing condomless sex among those at risk.