The findings are consistent with previous studies in showing that substance use behaviors co-occur and are more likely among youth with antisocial behaviors. Substance use and antisocial behaviors co-occurred with depression, truancy, and high-risk sexual behavior. Fewer previous studies have produced this finding; and this study is apparently distinctive in finding that the aforementioned behaviors co-occur significantly with obesity, extreme dieting, and failure to use bike helmets and seatbelts. Antisocial behavior co-occurred more often with other behaviors in 8th grade than in 11th grade. Positive behaviors were not as interrelated as problem behaviors, and were not strongly related to fewer problem behaviors. This suggests that efforts to promote positive youth development may have a limited impact in preventing problem behaviors. The study calculated binary indicators of 23 negative behaviors and 7 positive behaviors for 22,898 8th-grade and 15,828 11th-grade students who participated in the Oregon Healthy Teens Survey across 2 years of the survey (2001, 2002). Specific negative behaviors were grouped under the following categories: substance use, antisocial behavior, sexual behavior, depression, eating disorder, safety measures, and poor use of time. The positive behaviors measured were related to physical activity, volunteer services, participation in sports, participation in religious activities, doing chores, doing homework, and making good grades in school. 2 figures, 5 tables, and 37 references