Aims: The aims of this study were to explore time-based trends of socioeconomic differences in alcohol use and drunkenness in Finnish adolescents from 1990 to 2014 and to investigate the significance of two indicators in detecting socioeconomic differences in alcohol use and drunkenness. Methods: Data were retrieved from seven surveys conducted as part of the Health Behaviour in School-aged Children (HBSC) study in Finland from 1990 to 2014. The alcohol use and drunkenness of 15-year-old students, as well as socioeconomic status, including educational aspiration and perceived family wealth, were assessed via a self-report questionnaire. Logistic regression models were used to investigate the relationships between alcohol use, drunkenness and indicators of socioeconomic status. Results: The study showed that the alcohol use and drunkenness of Finnish 15-year-old adolescents have decreased since the late 1990s. However, the level of decrease is not consistent among different socioeconomic groups and socioeconomic differences in drinking behaviour between two educational aspiration groups have persisted over two decades. Girls from the groups with low perceived family wealth were more likely to be frequently drunk in the time period 2006–2014. Conclusions: This study suggests that students with low educational aspiration should be the target population for interventions aiming at reducing the alcohol use and drunkenness of Finnish adolescents. In future interventions aimed at reducing heavier drinking, adolescents (especially girls) from less wealthy families should be the first priority. Further studies on trends in socioeconomic differences in alcohol use and drunkenness in adolescence should be conducted using different indicators of socioeconomic status and other social context factors should also be taken into account.