BACKGROUND: The present study tested the co-occurrence of alcohol use and the first lapse and relapse into smoking among daily smoking adolescents who quit smoking. METHODS: In this ecological momentary assessment study, participants completed web-based questionnaires three times a day during one week prior to and three weeks after a quit attempt in their own natural environments. Participants were 134 daily smoking adolescents in the aged 15-19. Hierarchical linear modeling was applied to test whether alcohol use was related to the first lapse and relapse. Lapse was defined as the first incidence of smoking after achieving 24-h abstinence, relapse was defined as smoking at least five cigarettes on three consecutive days. RESULTS: The first lapse was strongly associated with alcohol use. Individual characteristics (age, sex, and baseline smoking status) did not predict the first lapse nor did they moderate the association between alcohol use and the first lapse. Progression from lapse to relapse did not seem to be associated with alcohol consumption, although this association appeared to be moderated by baseline smoking status. More specifically, alcohol use only posed a significant risk factor for relapse among those who smoked less frequently before the start of the study than others who relapsed. Intermittent smoking between the first lapse and relapse (or end of data) was strongly associated with alcohol use. CONCLUSIONS: Adolescent drinking during smoking cessation seems to be associated with the first lapse into smoking after quitting and subsequent intermittent smoking and should be targeted in adolescent smoking cessation interventions.