AIMS: To test whether (i) drinking motives predict the frequency of pre-drinking (i.e. alcohol consumption before going out); (ii) drinking motives predict HDGE (heavy drinking on a given evening: 4+ for women, 5+ for men) and related adverse consequences (hangover, injuries, blackouts, etc.), even when pre-drinking is accounted for, and (iii) drinking motives moderate the impact of pre-drinking on HDGE and consequences. DESIGN: Using the internet-based cellphone-optimized assessment technique (ICAT), participants completed a series of cellphone questionnaires every Thursday, Friday and Saturday evening over 5 weeks. SETTING: French-speaking Switzerland. PARTICIPANTS: A total of 183 young adults [53% female, mean age (standard deviation) = 23.1 (3.1)] who completed 7828 questionnaires on 1441 evenings. MEASUREMENTS: Drinking motives assessed at baseline, alcohol consumption assessed at 8 p.m., 9 p.m., 10 p.m., 11 p.m. and midnight and consequences assessed at 11 a.m. the next day. FINDINGS: Gender-separate multi-level models revealed that pre-drinking predicted HDGE (men: B = 2.17, P < 0.001; women: B = 2.12, P < 0.001) and alcohol-related consequences (men: B = 0.24, P < 0.01; women: B = 0.29, P < 0.001). Enhancement motives were found to predict HDGE (B = 0.48, P < 0.05) and related consequences (B = 0.09, P < 0.05) among men, while among women coping motives had the same effect (HDGE: B = 0.73, P < 0.001; consequences: B = 0.13, P < 0.01). With the exception of conformity motives among women (B = 0.54, P < 0.05), however, no drinking motive dimension predicted the frequency of pre-drinking, while coping and conformity motives moderated the impact of pre-drinking on HDGE (men, conformity: B = -1.57, P < 0.05) and its consequences (men, coping: B = -0.46, P < 0.01; women, coping: B = 0.76, P < 0.05). CONCLUSIONS: Among young adults in Switzerland, heavy weekend drinking and the related consequences seem to result from the combination of pre-drinking, level of negative reinforcement drinking for women and positive reinforcement drinking for men.