BACKGROUND: Overuse injuries result from microtrauma due to repetitive loading combined with insufficient tissue recovery time and can result in both immediate and long-term time loss from sports. HYPOTHESIS: Overuse injury rates and patterns differ across college and high school populations, sport, and sex. STUDY DESIGN: Descriptive epidemiology study. METHODS: Surveillance data for 16 sports from the National Collegiate Athletic Association's Injury Surveillance System (NCAA ISS; 2004-2005 through 2008-2009) and 14 sports from High School Reporting Information Online (High School RIO; 2006-2007 through 2012-2013) were analyzed. All reported injuries had an injury mechanism of overuse/gradual onset (college) or overuse/chronic (high school). Overuse injury incidence rates were calculated, and rate ratios with 95% CIs were used to compare subgroups. RESULTS: The rate of overuse injury was 3.28 times higher in college than high school sports (95% CI, 3.12-3.44). The rate of overuse injury among sex-comparable sports was higher in female than male athletes in both populations (college rate ratio, 1.25; 95% CI, 1.16-1.35; high school rate ratio, 1.55; 95% CI, 1.43-1.68). The lower extremity was the most commonly injured body site (college, 69.4%; high school, 70.4%). A larger proportion of overuse injuries among college athletes resulted in time loss of more than 21 days (college, 20.4%; high school, 7.7%) and surgery (college, 5.2%, high school, 2.5%). CONCLUSION: Overuse injuries can impose a significant burden on college and high school athletes. Interventions addressing prevention of overuse injury are needed.