There are numerous abnormalities that present with similar signs and symptoms to arthritis. In this article some of these conditions that can masquerade as arthritis are discussed. Synovial osteochondromatosis is an uncommon benign disorder marked by the metaplastic proliferation of multiple cartilaginous nodules in the synovial membrane of the joints, bursae, or tendon sheaths. Pigmented villonodular synovitis, also known as diffuse-type tenosynovial giant cell tumor, is a locally destructive fibrohistiocytic proliferation, characterized by many villous and nodular synovial protrusions which affects the joints. Synovial hemangioma is a rare benign lesion whose pathogenesis is still unclear. It commonly affects the knee joint, although the other articulations, such as elbow, wrist, and ankle may also be involved. Lipoma arborescens, also known as villous lipomatous proliferation of the synovial membrane, is a rare intra-articular disorder characterized by a non-neoplastic lipomatous proliferation of the synovium. The term “arborescens” refers to the characteristic tree-like morphology of the lesion, which resembles a frond-like mass.