AIMS:To test the efficacy of the Tobacco Status Project (TSP) Facebook smoking cessation intervention for young adults relative to referral to an on-line program on biochemically verified 7-day abstinence from smoking. DESIGN:Two-group parallel randomized controlled trial, comparing TSP (n = 251) to on-line control (n = 249) with follow-up to 12 months. SETTING:On-line, throughout the United States. PARTICIPANTS:Young adult cigarette smokers (mean age 21 years; 73% white, 55% female, 87% daily smokers). INTERVENTIONS AND COMPARATOR:TSP provided private Facebook groups tailored to stage of change to quit smoking, daily contacts, weekly live counseling sessions, and for those ready to quit, six cognitive behavioral therapy counseling sessions. Some TSP groups were assigned randomly to receive a monetary incentive for engagement. Control provided referral to the National Cancer Institute Smokefree.gov website. MEASUREMENTS:PRIMARY OUTCOME: Biochemically verified 7-day abstinence over 12 months. SECONDARY OUTCOMES:Post-treatment (3-month) abstinence; reported abstinence, quit attempt, reduction in smoking, readiness to quit smoking over 12 months. FINDINGS:Verified 7-day abstinence was not significantly different for intervention compared with control over 1 year: month 3 (8.3 versus 3.2%), 6 (6.2 versus 6.0%), and 12 (5.9 versus 10.0%); odds ratio (OR) = 1.07; 95% confidence interval (CI) = 0.23, 4.97; retention = 71%. There was an effect at 3 months (OR = 2.52; CI = 1.56, 4.04; P < 0.0001). There were no 12-month treatment effects for reported abstinence (P = 0.746), reduction in smoking by 50% or more (P = 0.533), likelihood of having made a quit attempt (P = 0.387) or stage of change over time (0.968). Participants in TSP engaged more and rated the intervention more favorably than those in the control condition. CONCLUSIONS:Compared with referral to a smoking cessation website, a novel USA-focused Facebook smoking cessation intervention did not improve abstinence from smoking over 1 year, but increased abstinence at the end of treatment and was engaging to participants.