Expectancy challenges (ECs) were used to change alcohol expectancies and alcohol consumption in young heavy drinking men (age 16-24) on holiday. The intervention took place in community centers and bars. Alcohol expectancies and consumption were assessed with paper and pencil measures prior to the intervention (N=301) and 2 days afterwards (EC: n=178; controls: n=86). Six weeks after the EC,, participants were interviewed by telephone (EC: n = 163; controls: n =71). The intervention resulted in an increase in sedation expectancies in the EC group. Furthermore, the EC led to a differential reduction in alcohol consumption on a night out at the six-week posttest in the heaviest drinkers only. The reduction in alcohol consumption on a night out was not mediated by the change in sedation expectancies. These findings suggest that further research on the mechanisms of change is necessary before a single-session EC may be used in a real-life prevention setting.