Objective: A person's pattern of heavier drinking often changes over time, especially during the early drinking years, and refl ects complex relationships among a wide range of characteristics. Optimal understanding of the predictors of drinking during times of change might come from studies of trajectories of alcohol intake rather than crosssectional evaluations. Method: The patterns of maximum drinks per occasion were evaluated every 2 years between the average ages of 18 and 24 years for 833 subjects from the Collaborative Study on the Genetics of Alcoholism. Latent class growth analysis identifi ed latent classes for the trajectories of maximum drinks, and then logistic regression analyses highlighted variables that best predicted class membership. Results: Four latent classes were found, including Class 1 (69%), with about 5 maximum drinks per occasion across time; Class 2 (15%), with about 9 drinks at baseline that increased to 18 across time; Class 3 (10%), who began with a maximum of 18 drinks per occasion but decreased to 9 over time; and Class 4 (6%), with a maximum of about 22 drinks across time. The most consistent predictors of higher drinking classes were female sex, a low baseline level of response to alcohol, externalizing characteristics, prior alcohol and tobacco use, and heavier drinking peers. Conclusions: Four trajectory classes were observed and were best predicted by a combination of items that refl ected demography, substance use, level of response and externalizing phenotypes, and baseline environment and attitudes.