Primary synovial chondromatosis (SC) is a rare proliferative disorder that causes pain, swelling, and restriction of movement to the joints it affects. The disease frequently runs a protracted course, often requiring multiple surgical procedures to obtain some control. Few reports exist detailing the natural history of SC, although malignant transformation to synovial chondrosarcoma (CHS) is recognized to be a rare event. The aim of our study was to review a large orthopaedic oncology database in order to evaluate the incidence of CHS arising from SC. We identified 78 patients who have presented to our centre with primary synovial chondromatosis (SC). Of those patients, 5 went on to develop malignant change. This represents a 6.4% incidence of developing synovial chondrosarcoma (CHS) within preexisting primary synovial chondromatosis. The patients had a mean age of 28 years at first diagnosis with synovial chondromatosis with the median time from original diagnosis to malignant transformation being 20 years (range 2.7-39 yrs).