This report presents a 16 year old girl with persistent left knee pain caused by an intra-articular synovial lipoma (IASL) of the knee. Arthroscopy revealed a lipoma arising from the posterior aspect of the synovial membrane, extending in the femoral intercondylar notch, between the femoral attachments of anterior cruciate ligament and posterior cruciate ligament. Histological examination confirmed the diagnosis of IASL. IASL is a rarely described situation. There are only a few references in the literature. One IASL found in an adolescent and one more located in the intercondylar notch have been described.