Mucormycosis accompanied the development of bacterial infection in the leg of a diabetic African-American man. Local injury, diabetic ketoacidosis, renal insufficiency, and antimicrobial therapy were factors that contributed to the pathogenesis of the mucormycosis. The cellulitis was caused in part by Rhizopus microsporus var. microsporus and was cured by amputation. We report this unusual case of mucormycosis to emphasize the value of fungal identification, to illustrate a dramatic and successful clinical result, and to draw attention to an apparent role for bacterial infection and its treatment in the pathogenesis of mucormycosis. It is the third case report of mucormycosis in a human in which R. microsporus var. microsporus was definitively identified as the etiologic agent.