This study examines smoking behavior in a sample of 231 opioid-dependent clients entering therapeutic community treatment, and investigates the relationship between smoking behavior and drug treatment outcomes. We applied regression analyses for selected Addiction Severity Index composites (alcohol, drug, medical, psychiatric), including factors for smoking (number of cigarettes per day, expired-air carbon monoxide level, nicotine dependence), time (baseline, 6 and 12-month), and smoking-by-time interaction. This study confirmed a high smoking prevalence (95%) among opioid users. Among participants interviewed at all time points (n = 206), 13% shifted from smoking to non-smoking status at some time after admission. Participants who reported a greater number of cigarettes were more likely to report higher drug severity at any time point.