Efficacy of bupropion SR and individual counseling as smoking cessation treatments was assessed in a randomized, placebo-controlled clinical trial among adult daily smokers. Bupropion SR treatment and counseling were fully crossed in this factorial design so that the efficacy of each treatment and the combination could be estimated, relative to a placebo medication and assessment control condition. Intent-to-treat analyses indicated that bupropion SR increased abstinence rates at the end of treatment, relative to the placebo medication conditions, for both biochemically confirmed 7-day point-prevalence abstinence (OR = 1.97, 95% CI 1.04-3.72) and self-reported prolonged abstinence (OR = 2.90, 95% CI 1.66-5.06). Bupropion SR treatment also improved latency to lapse and relapse and improved the latency between lapse and relapse in survival analyses. Medication effects were more modest for both 12-month point-prevalence abstinence (OR = 1.47, 95% CI 0.74-2.92) and prolonged abstinence (OR = 1.34, 95% CI 0.66-2.72). Counseling was not associated with increases in the likelihood of abstinence at any time point (odds ratios ranged from 0.80 to 1.16 across abstinence outcomes in the full intent-to-treat sample). Counseling and medication did not significantly interact at any time point, and adding counseling did not improve end-of-treatment point-prevalence abstinence (OR = 1.17, 95% CI 0.68-2.03) or prolonged abstinence (OR = 1.26, 95% CI 0.75-2.12) substantially when offered in conjunction with active medication.