A chronic expanding hematoma (CEH) is a rare clinicopathologic entity that may simulate the clinical and radiologic presentation of soft tissue sarcomas. Etiology has been attributed to repeated exudation and bleeding from capillaries in granulation tissue, resulting in a gradually enlarging mass. A 51-year-old male presented with a large thigh mass following a gunshot wound one year prior. Diagnostic imaging revealed a large complex mass with cystic areas overlying cortical erosions in the femoral diaphysis suggestive of osteomyelitis versus a primary aggressive new growth. Biopsy confirmed CEH and the absence of malignant cells. Hip disarticulation was performed after noting massive necrosis of the thigh compartments and neurovascular compromise. CEH is an important differential diagnosis to be considered in a patient with a slow-growing soft tissue mass and history of significant trauma. Its similar clinical presentation with a soft tissue sarcoma necessitates a high index of suspicion, diagnostic imaging, and biopsy prior to performing definitive surgery.