Over a period of 6 months, factors related to change in cigarette smoking were investigated in a group of 250 adult outpatients, all of whom smoked at the time of enrollment in the study. Among the variables tested were demographic, social, and situational factors, beliefs about the health effects of smoking and difficulty of quitting, and intentions regarding future smoking. Information was gathered at baseline and the first and sixth months by means of telephone interviews. Relative to smoking at 6 months, intention, education, and professional advice made independent contributions to cessation. The processes of quitting were examined in more detail. Attempting to quit was related to intention, professional advice, level of smoking, and social cues to smoke. Among those who tried to stop, difficulty with urges to smoke, and education affected success versus failure. Earlier success related to less anxiety and tension, and to less difficulty in not smoking when in negative situations. The findings suggest that a complex set of social and cognitive factors affect change in smoking behavior, and that somewhat different factors are operative at different stages.