A 52-year-old woman presented with load-dependent pain on the right knee. Pressure pain was conceived at the medial femoral condyle and manual valgus stress as well as rotation provoked severe pain at the medial side of the knee. Plain radiographs showed an ossification at the proximal part of the medial collat eral ligament (Fig. A). Further imaging occurred. Magnetic Resonance Imaging (MRI) showed the ossification as a signal void on T2- weighted images (Fig. B-C). There was also a hyper-intense signal surrounding the medial collateral ligament on T2-weighted images, consistent with an acute component. The diagnosis Pellegrini Stieda disease was made. Therapy consisted of rest and the use of non-steroidal anti-inflammatory drugs to treat the acute inflammatory component. No further follow-up of the patient occurred.