This study examined the association between stopping smoking at 1 year after substance use treatment intake and long-term substance use outcomes. Nine years of prospective data from 1185 adults (39% female) in substance use treatment at a private health care setting were analyzed by multivariate logistic generalized estimating equation models. At 1 year, 14.1% of 716 participants who smoked cigarettes at intake reported stopping smoking, and 10.7% of the 469 non-smokers at intake reported smoking. After adjusting for sociodemographics, substance use severity and diagnosis at intake, length of stay in treatment, and substance use status at 1 year, those who stopped smoking at 1 year were more likely to be past-year abstinent from drugs, or in past-year remission of drugs and alcohol combined, at follow-ups than those who continued to smoke (OR=2.4, 95% CI: 1.2-4.7 and OR=1.6, 95% CI: 1.1-2.4, respectively). Stopping smoking at 1 year also predicted past-year alcohol abstinence through 9 years after intake among those with drug-only dependence (OR=2.4, 95% CI: 1.2-4.5). We found no association between past-year alcohol abstinence and change in smoking status at 1 year for those with alcohol dependence or other substance use diagnoses when controlling for alcohol use status at 1 year. Stopping smoking during the first year after substance use treatment intake predicted better long-term substance use outcomes through 9 years after intake. Findings support promoting smoking cessation among smoking clients in substance use treatment.