Objectives The aim of the present study was to investigate the efficacy of a brief coping planning intervention to prevent smoking relapse in the context of a national smoking cessation contest (‘Quit & Win’).

Design A controlled trial with three measurements was used to evaluate the efficacy of the coping planning intervention.

Methods Three on-line surveys were conducted among 1,566 participants in Quit & Win. Contest participants were alternately assigned to a control and planning group, the latter of which completed a planning intervention that included the formation of three coping plans on how to refrain from smoking in personal risk situations.

Results The coping planning intervention increased conservative 7-month continuous abstinence rates from 10.5 to 13.4%, indicating that, if implemented correctly, coping planning can significantly reduce long-term smoking relapse.

Conclusions In addition to growing evidence for the efficacy of self-regulatory planning in the promotion of health behaviour, the results of the present study indicate that planning can also be effective in the prevention of unwanted behaviour. The results may stimulate research and application of coping planning in its current form.