A prospective design was used to determine the outcomes associated with unaided smoking cessation and the influence of stress on cessation. Heavy smokers (N = 308) completed stress-related measures and were then recontacted at 1, 6, and 12 months. At each follow-up, they indicated their smoking status (which was confirmed by collateral report and biochemical tests) and completed several stress-related questionnaires. Results indicated that 33% of subjects smoked continuously throughout the year, 39% quit briefly but subsequently relapsed, and 15% quit (confirmed biochemically). An additional 7% reported that they had quit, but this could not be confirmed, and 6% were lost to follow-up. Compared with nonquitters, quitters reported less perceived stress, greater self-efficacy, greater use of problem solving and cognitive restructuring, and less reliance on wishful thinking, self-criticism, and social withdrawal. A model to forecast quitting was built and cross-validated.