To better understand why most persons in drug treatment smoke, we explored patients' views of the relationship between their smoking, methadone, and drug use. Recruiting from four methadone clinics, we held seven focus groups with 68 current smokers, and 10 individual interviews with former smokers. Sessions were audio-taped, transcribed, and coded. Participants were > or =18 years old, smoked > or =5 cigarettes per day, and had used prescription methadone for > or =2 years. Most patients linked smoking, methadone, and drug use in three ways. First, patients said smoking and drug use were complementary. Examples included smoking to reduce methadone after taste and using drugs to reduce smoking-related throat pain. Second, smoking and drug use were similar because they shared cues and withdrawal symptoms. Third, smoking differed from drug use because it had fewer acute consequences. Because smoking, methadone, and drug use are closely interrelated, future addictions research and treatment protocols should address them in combination.