A 50-year-old woman presented with a slightly tender mass on the postero-lateral aspect of her thigh. The mass had been present for approximately 10 years and had slowly increased in size, causing a minor degree of discomfort when sitting on a hard seat. On examination, a diffuse tender swelling, approximately 5 cm × 3 cm, was present on the postero-lateral aspect of the thigh. Apart from a small melanoma on the postero-lateral aspect of the other thigh, no other abnormality could be found. Plain radiographs of the femur (Figs 1, 2) revealed a clearly defined, ovoid lucency in the midshaft with a breach of the cortex. A thin rim of sclerosis surrounded this area with a discrete layer of well organised periosteal reaction on the medial aspect of the femur overlying the lesion. A well defined soft-tissue mass lesion could just be delineated. The remainder of the femur was normal and no other similar lesions were found.