We reviewed the records and radiographs of seven children who presented with knee pain, local tenderness over the medial femoral condyle, and radiological irregularity of the distal medial metaphysis of the femur suggestive of malignancy. In the five patients who had biopsies, histological changes were consistent with musculotendinous avulsion, and the dissection of ten cadavers confirmed the site to be the insertion of part of the adductor magnus. The recognition of this lesion and knowledge of its benign nature may avoid unnecessary anxiety and needless biopsy.