Lipoma arborescens is a rare intra-articular lesion characterized by villous lipomatous proliferation of the synovial tissue, usually found in knee. Patients with this benign condition are seen with progressive, painless swelling of the joint. We presented a case of 35 year old man with 3 year history of painless swelling in right knee. The symptom waxed and waned having about 1 year interval. The swelling was not related to alcohol intake and walking. Physical examination revealed severe effusion in right knee. The active range of motion was full and patient explained some tenderness on lateral side of patello-femoral joint. There were no abnormalities in knee X-ray but magnetic resonance image revealed a villous proliferation in suprapatella pouch. There were no significant abnormalities in blood test. Joint fluid analysis did not reveal any cause of swelling and effusion. In evaluation of isokinetic exercise, there was significant weakness of knee extensors.
