Abstract
A 2-year-old boy had intermittent pain and mottling of the left thigh. Swelling of the vastus lateralis developed, and a biopsy revealed proliferative myositis. The pathogenesis is unknown, but trauma and ischemia have been implicated. The rarity of proliferative myositis in children, and the possibility of mistaking the lesion for a sarcoma make the case noteworthy.