Introduction Smokers receiving mental health care are particularly in need of tailored interventions. Objective Study of patients enrolled in a specialized smoking cessation program based upon a 26-hour smoking abstinence period aimed better understanding of self-efficacy for smoking cessation and of the decision to quit. Methods A logistic regression predicting success/failure of abstinence included different variables. Self-efficacy for temporary abstaining from smoking (TASE) and for permanent quitting (QSE) were distinguished. Results In 174 subjects enrolled at baseline, TASE was the only predictor of successful abstinence (OR=1.43; p=.001). Assessment of 138 subjects present 1 week after intervention showed increases in TASE and QSE (median TASE from 8 to 10, p<.0001; median QSE from 8 to 9, p=.02). In subgroups of successful abstainers and of those engaging into smoking cessation, only TASE increased. Interestingly, for subjects who had planned a quit attempt already before the intervention, 52% were still abstinent at 1 week vs. 87% of those who decided to quit during the intervention (p=.02). Conclusion A multicomponent program for all smokers can be a powerful method to increase self-efficacy, in particular for temporary smoking abstinence, and trigger unplanned quit attempts, shown here to be more successful than planned attempts.