Synovial chondromatosis is an uncommon disorder characterized by the formation of multiple cartilaginous nodules within the synovium and most commonly affects large joints, such as the knee and hip. Diagnosis in synovial chondromatosis is generally confirmed by histology after clinical and radiologic examination. Diagnosis may sometimes be difficult because synovial chondromatosis resembles a soft-tissue mass and may give no radiologic findings. We describe a case of synovial chondromatosis stemming from the subtalar joint, in which diagnosis was difficult clinically and radiologically. The patient presented with pain in the ankle and with a soft-tissue mass. This case is presented with a review of the literature on subtalar joint involvement of synovial chondromatosis.