Abstract: Primary synovial chondromatosis (PSC) is a rare, benign neoplastic disorder affecting otherwise healthy joints. It is characterized by formation of cartilaginous nodules in the synovial lining. These nodules can detach from the synovium and evolve to numerous intra-articular loose bodies, which may be calcified or not. On conventional radiography, calcified nodules are readily visible in most cases but uncalcified nodules may remain unrecognized. MRI has a higher sensitivity for detecting uncalcified PSC but also for detecting bone erosions. In addition, MRI is the modality of choice to exclude bone marrow invasion, suggestive of a malignant lesion, which is extremely rare. On histopathology, PSC may show cytologic atypia, possibly making differentiation from low-grade synovial chondrosarcoma (SChS) difficult. Correlation of clinical, radiologic, and histologic findings is therefore pivotal to avoid misdiagnosis, which could lead to harmful treatment. The intra-articular bodies in secondary synovial chondromatosis (SCC) originate from detached cartilage secondary to nonneoplastic joint abnormalities such as degenerative joint disease, trauma, or other diseases causing cartilage damage. Histopathologic examination is able to differentiate primary and secondary forms in rare cases of nonspecific imaging features. This chapter focuses on the imaging features of PSC and SCC and its relevant differential diagnosis.