BackgroundIntra-articular lipomas are rare and very few cases have been reported in the knee. To the best of our knowledge, here we report the largest lipoma to have ever been observed in the knee. It is crucial to avoid the misdiagnose of lipoma arborescens, which is associated with degenerative joint disease. Lipoma is a homogeneous, ovoid, adipose tissue tumor that is contained within a fibrous capsule and not associated with previous disease.Case presentationA 48-year-old male, with a soft-tissue tumor on the superomedial aspect of the right knee. Magnetic resonance imaging (MRI) revealed an intra-articular lipoma. The mass was resected by means of a limited arthrotomy.ConclusionsKnee lipoma is an extremely rare disease that must be diagnosed by MRI. Where possible, it should be resolved by arthroscopic resection.