Background:The frequency of osteochondritis dissecans (OCD), a disorder of the subchondral bone and articular cartilage, is not well described.Purpose:To assess the frequency of pediatric OCD lesions that progress to surgery based on sex, joint involvement, and age.Study Design:Descriptive epidemiology study.Methods:A retrospective chart review (2007-2011) was performed on OCD. Inclusion criteria included OCD of any joint and patients aged 2 to 19 years. Exclusion criteria included traumatic osteochondral fractures or coexistence of non-OCD intra-articular lesions. Differences in progression toward surgery were compared between age groups, sex, and joint location. Logistical regression analysis was performed by sex, age, and ethnicity.Results:Overall, 317 patients with a total of 334 OCD lesions were found. The majority of lesions (61.7%) were in the knee, with ankle, elbow, shoulder, and foot lesions representing 25.4%, 12.0%, 0.6%, and 0.3% of all lesions, respectively. The majority of joints needing surgery were in the knee (58.5%), with ankle and elbow lesions representing 22.9% and 18.6% of surgeries performed, respectively. The percentage of all OCD lesions progressing to surgery was 35.3%; surgical progression for knee, ankle, and elbow joints was 33.5%, 31.8%, and 55.0%, respectively. Logistic regression analysis found no statistically significant different risk of progressing to surgery for OCD of the knee, elbow, and ankle between sexes. Patients aged 12 to 19 years had a 7.4-times greater risk of progression to surgery for knee OCD lesions than 6- to 11-year-olds. Patients aged 12 to 19 years were 8.2 times more likely to progress to surgery for all OCD lesions than patients aged 6 to 11 years. Progression to surgery of ankle OCD did not significantly differ based on location. Three of 4 trochlear lesions progressed to surgery, along with 1 of 1 tibial, 1 of 3 patellar, 40.3% of lateral femoral condylar, and 28.2% of medial femoral condylar lesions.Conclusion:In this large cohort study of pediatric OCD patients, 35% progressed to surgery. Progression to surgery did not differ significantly between sexes with OCD of any joint. Progression to surgery for OCD of the knee, elbow, and ankle strongly correlated with patient age at the time of diagnosis.Clinical Relevance:The knowledge of likelihood of progression to surgery of OCD by location, sex, and age is useful in counseling patients and in planning treatment. This study confirms a worse prognosis in the nonoperative treatment of older patients with OCD.