Adolescent drinking behavior was observed on weekend nights (9 PM until midnight) in three youth bars, three youth centers and two discos located in the most southern part of the Netherlands. Drinking rates, individual characteristics, drinking group variables and aspects of the overall drinking situation were recorded. Boys and girls appeared to differ in the variables of influence on their drinking rates. Boys were observed to drink at a higher rate on evenings with loud music, when they participated in large, all-male groups and when their (estimated) age was less than 20. Together these variables explain 24% of the variance in boys' drinking rates. Girls drank less fast when they participated in a group not buying rounds and in a drinking group of constant composition. Although analysis showed that girls' drinking rates did not vary significantly with aspects of the overall situation and individual variables, still 14% of the total variance here could be explained by the drinking group variables. These results are to some extent consistent with findings from other observational studies on drinking behavior. Most of these studies showed males in large groups to drink at the highest rates. However, only a few observational studies were aimed exclusively at young people's drinking behavior and those studies did not include aspects of the overall drinking situation.