This study evaluated the relationship between precessation depressed mood and smoking abstinence and assessed the mediation of this effect by postcessation self-efficacy, urges to smoke, nicotine withdrawal, and coping behavior. The sample included 121 smokers previously treated in a randomized controlled trial involving behavior therapy and the nicotine patch. The results showed that precessation depressed mood was inversely related to 6-month abstinence. This effect remained significant after controlling for treatment, possible depression history, baseline smoking rates, and several other demographic factors. Postcessation self-efficacy, at the 2-, 4-, and 8-week postquit assessments, was the strongest mediator of the effects of precessation depressed mood on abstinence, accounting for 32%, 38%, and 48% of the effect of mood on abstinence, respectively.