Abstract: Objective : To investigate the early diagnosis of osteosarcoma for patients with negative X-ray presenta-tion. Methods : We reviewed the clinical symptoms of 9 osteosarcoma patients who were negative upon X-rayexamination. The data we analyzed included results of X-ray, computerized tomography (CT), magnetic reso-nance imaging (MRI), serological examination and needle biopsy. The 9 osteosarcoma patients included 7males and 2 females. Seven cases had tumors in the distal end of the femur and 2 cases had tumors in theproximal end of tibia. The patients'age ranged from 14 to 33 years, with an average of 19.8 years. The pa-tients'chief complaint was indisposition of the knee joint and their symptoms lasted from 20 to 55 days, withan average of 39 days. Results : All 9 patients with osteosarcoma underwent X-ray examination, without posi-tive indications. Six patients underwent CT scan and 2 of them (33.3%) showed a possibility of osteosarcoma.The serum level of alkaline phosphatase exceeded the normal range in 4 cases (44.4%). Seven cases hadneedle aspiration biopsy, which confirmed the disease. All of the patients underwent MRI scan and the resultsindicated osteosarcoma, with a diagnosis rate of 100%. Eight cases had irregular low signals in T1WI and theboundary was acceptable. One case had irregular low signals in T1WI and T2WI and bright contrast with sur-rounding constit. None of the cases had obvious cortical destruction. Conclusion : Early stage osteosarcomamay not be apparent upon X-ray examination. Osteosarcoma should be considered in young patients withpain in the vicinity of the knee joint without any history of injury. MRI scan or needle aspiration biopsy shouldbe employed to obtain the final diagnosis.