This article reports long-term trends by race/ethnicity and socioeconomic status (SES) in the percent of American students who are overweight and who engage in three health-related behaviors hypothesized to be associated with overweight.Data are from the Monitoring the Future annual surveys, using nationally representative samples of eighth, 10th, and 12th grade students. Participants include 62,156 eighth and 64,899 10th graders who completed the 1993-2003 surveys and 35,107 12th graders who completed the questionnaire form containing the measures pertaining to this study in the 1986-2003 surveys. Trends are presented separately by gender and grade level for different racial/ethnic and SES subgroups, in: (a) percent overweight (body mass index > or = 85th percentile), (b) percent who always or almost always eat breakfast, (c) percent who regularly exercise vigorously, and (d) average hours of weekday television viewing.The prevalence of overweight and of engaging in less healthy behaviors is considerably greater among youth from racial/ethnic minority backgrounds, of lower socioeconomic status, and in higher grades. Trends in overweight and these behaviors are found to vary substantially by gender, racial/ethnic group, socioeconomic status, and grade level.The study findings show well-established and persistent differences in the percent of racial/ethnic minority and low SES youth who are overweight and whose dietary and exercise habits are less healthy. Documentation of these problems may lead to research and policy agendas that will contribute both to our understanding and to the reduction of these important health disparities.