Lipoma arborescens (synovial lipomatosis) is a rare, benign intra-articular lesion of unknown etiology. It is a very rare primary benign tumour of the synovium, which usually affects the knee joint and can lead to slowly progressive chronically swollen knee. In this report we described two cases with this rare entity with initial presentation of inflammatory synovitis. We also described the Gadolinium (Gd-DTPA)-enhanced MRI features. To the best of our knowledge, this is the first report that described inflammatory synovitis in association with this rare entity.