Positive alcohol expectancies and alcohol use tend to increase from adolescence to young adulthood, yet little is known about the associations between these constructs across cultures. The current study adds to the extant literature by examining the growth trajectories of positive alcohol expectancies and drinking behavior among United States (US) and Swedish participants during a critical period where significant change in these outcomes may be expected to occur. A total of 870 (US, N = 362; Sweden, N = 508) high school seniors completed baseline, 6-month, and 12-month assessments of alcohol expectancies and drinking (i.e., drinks per week). Changes in positive alcohol expectancies and drinking behavior were examined using a parallel process latent growth model. In both samples, higher baseline levels of positive alcohol expectancies were associated with a higher number of drinks consumed per week at baseline. In the US sample, lower baseline levels of positive alcohol expectancies were associated with a greater increase in positive alcohol expectancies at 12-month follow-up, and lower baseline levels of drinks per week were associated with a greater increase in drinks consumed per week at 12-month follow-up. In the Swedish sample, an increase in positive alcohol expectancies over time was associated with an increase in drinks consumed per week over the same period of time. Additional research is needed to examine when and for whom expectancy-based alcohol interventions are most efficacious.