Data were collected from 4,698 adolescents in the 1994 survey, 4,595 adolescents in the 1995 survey, and 4,538 adolescents in the 1996 survey. Adolescents were asked to provide self-reports of their competencies and problems in order to assess depression, anxiety, social withdrawal, somatic complaints, social problems, thought problems, attention deficits, delinquent behavior, and aggressive behavior. Past-year marijuana users were more likely than non-users to report problem behaviors during the past 6 months. For the majority of items measured, the more frequent the marijuana use, the more likely adolescents were to report problem behaviors. More frequent marijuana users were likely to be older, white, male, and to have lived in metropolitan areas and the western part of the United States. In addition, more frequent marijuana users were more likely than less frequent marijuana users to have moved in the past year and were less likely to live in two-parent families. Frequent marijuana users were less likely than less frequent marijuana users to report delinquent behaviors such as running away from home, stealing, and cutting classes or skipping school. They were also more likely to report aggressive behaviors such as destroying things that belonged to others and physically attacking people. Monthly or more often marijuana users were more likely than less frequent marijuana users to have driven under the influence of alcohol or drugs or sold illegal drugs during the past year. From a psychological view, adolescents who used marijuana during the past year reported many behaviors symptomatic of anxiety and depression. The findings strengthen the argument that marijuana is not a benign substance. 18 references and 11 tables