Diagnostic knee arthroscopic findings in 70 children aged 7-18 years with acute traumatic knee hemarthroses showed a high incidence of intraarticular lesions. Forty-seven percent of preadolescents (aged 7-12 years) had meniscal tears, and 47% had anterior cruciate ligament (ACL) tears. Forty-five percent of adolescents (aged 13-18 years) had meniscal tears and 65% had ACL tears. Osteochondral fractures accounted for 7% of the lesions. Meniscal and ACL pathology is common in children, especially adolescents. Because arthroscopy provided accurate diagnosis, specific treatment could be instituted.