What tests should a patient undergo if he/she suspects osteosarcoma and which is better to diagnose osteosarcoma, MRI or X-ray? The Practical Orthopedics (2nd edition) later clearly states that osteosarcoma can be diagnosed by X-rays. However, some early-stage intramedullary osteosarcomas cannot be detected by X-ray and require MRI as an adjunct. It is important to know that the imaging lesion manifestation of MRI is 6~8 months earlier than X-ray, and MRI is more accurate than X-ray examination in diagnosing intraosseous lesions. As for bone scan examination, it can assist in diagnosing whether the tumor has developed metastasis or the presence of jumping lesions. However, X-ray and MRI are mandatory tests to be completed in the initial diagnosis of osteosarcoma, while bone scan examination is not necessary. Is an elevated serum alkaline phosphatase diagnostic of osteosarcoma? Elevated serum alkaline phosphatase reflects the number of osteoblasts in the body and is only an indirect indicator for the diagnosis of osteosarcoma. It is important to know that many children have an increase in alkaline phosphatase during adolescent growth. Therefore, alkaline phosphatase is not a necessary tool to confirm the diagnosis of osteosarcoma; however, it can provide information about osteosarcoma, for example, when alkaline phosphatase is particularly high, reaching 500-600 U/L, we need to be highly suspicious of osteosarcoma. Do all suspected osteosarcomas require pathological testing? The answer is yes. Because the pathological diagnosis result of osteosarcoma can make the treatment targeted, and it is even better if the pathological subtype is classified, which can help a lot in the follow-up treatment.