BACKGROUND: Osteosarcoma is the most common malignant bone tumor in children and young adults. Since the introduction of chemotherapy, the 5-year survival rate of patients with non-metastatic osteosarcoma is ~70%. The main problems in osteosarcoma therapy are the occurrence of metastases, severe side-effects and chemoresistance. Antiproliferative and apoptotic effects of quercetin were shown in several types of cancers, including breast cancer and lung carcinoma. MATERIALS AND METHODS: The present study investigates the cytotoxic potential of quercetin, a dietary flavonoid, in a highly metastasizing human osteosarcoma cell line, 143B. RESULTS: We found that quercetin induces growth inhibition, G2/M phase arrest, and apoptosis in the 143B osteosarcoma cell line. We also observed impaired adhesion and migratory potential after the addition of quercetin. CONCLUSION: Since quercetin has already been shown to have low side effects in a clinical phase I trial in advanced cancer patients, this compound may have considerable potential for osteosarcoma treatment.