Lipoma arborescens is a rare benign fat-containing synovial proliferative lesion that is typically known to affect the knee joint in adults. We present the first case of lipoma arborescens of the ankle joint in an adult patient with involvement of the intra-articular synovium as well as the synovial sheath of the tendons around the ankle. The MRI features of this lesion in the adult ankle are described.