Abstract: To compare clinical differences between preadolescent and young adult osteosarcoma patients and identify the prognostic factors of the disease. Methods: The clinical data of 107 osteosarcoma patients younger than 19 years were retrospectively reviewed. The data obtained covered the period from October 2003 to March 2010, and included sex, age, tumor site, etc. The mean follow-up time was 26.1 months ( ranged from 3 to 82 ). χ2 methods and Fisher exact methods were used to compare clinical differences between preadolescent and young adult patients. The Kaplan-Meier method was used to measure the overall survival rate. A log-rank univariate analysis was used to determine the prognostic factors related to the survival rate. The Cox model multivariate analysis was used to identify independent prognostic factors. Results: The median survival time of 107 patients in the present study was 34 months ( 95% CI: 18.5 to 49.5 ). The 1- and 2-year cumulative survival rates were ( 85 ± 4 ) % and ( 59 ± 5 ) %, respectively. No significant difference between preadolescents and young adults in terms of sex, Enneking stage, KPS  score, pathological fracture, tumor necrosis rate, histologic type, tumor location, frequency of adjuvant chemotherapy, and tumor size was found. However, more preadolescent patients received amputation surgery. Log-rank univariate analysis showed that the significant factors were the Enneking staging, KPS score, frequency of adjuvant chemotherapy, and occurrence of metastasis. Cox regression analysis revealed that the KPS score, frequency of adjuvant chemotherapy, and occurrence of metastasis were the prognostic factors of preadolescent and young adult osteosarcoma. No significant difference between age, sex, tumor site, tumor size, Enneking staging, neoadjuvant chemotherapy, local recurrence, and pathological fracture was found. Conclusion: The clinical characteristics and survival rates of preadolescents and young adults with osteosarcoma in China were similar. The KPS score, frequency of adjuvant chemotherapy, and occurrence of metastasis were the prognostic factors of osteosarcoma.