BACKGROUND: Organized sport is viewed as a viable medium for promoting more physical activity among youth. However, participation in youth sport declines significantly among both boys and girls during their middle school years. This study examined middle school students' perceived constraints to sport participation. METHODS: Middle school students from 4 schools (6th-8th grade, N = 2465) completed a web based survey (97.3% response rate). Descriptive analysis, t tests, and ANOVA were used to assess extent of perceived constraints and differences among demographic and sport participation level subgroups. RESULTS: The most salient constraint perceived by respondents was time, while knowledge was perceived as the lowest among the overall sample. Significant (P < .01) differences in perceived constraints were found among all comparisons groups. Girls, Latinos, lower SES students, and students who did not play sports reported more constraints than respective comparisons groups. DISCUSSION: The sociodemographic characteristics of middle school students appear to be a significant factor in their perception of constraints to sport participation. Identifying constraints associated with sport participation can enable policy-makers and administrators to be more deliberate in channeling resources.