An eight-year-old boy presented with massive pseudomalignant heterotopic ossification around the upper femur. The mass was completely excised because of severe pain, systemic illness and a flexion contracture at the hip. Symptomatic improvement was swift, but two weeks later the mass had recurred and was even more extensive. During the subsequent 18 months of conservative management he has been free of pain and there has been progressive resorption and remodelling of the heterotopic bone. There is now no limitation of physical activity and movement at the hip is full.