We report the case of a 44-year-old white man who presented with progressively worsening crampy abdominal pain and distention. Deterioration of his clinical picture along with leukocytosis and radiographic evidence of severe colonic dilation rendered exploratory laparotomy necessary. Greatly distended and inflamed transverse and descending colon were evident and an extended left colectomy was performed. Characteristic changes of leukocytoclastic vasculitis in the serosal and muscular layers of the resected colon were demonstrated at histopathologic examination. Systemic leukocytoclastic vasculitis, usually coexisting with Henoch-Schonlein purpura, commonly affects the small bowel with clinical evidence of ischemia or bleeding. Colon involvement is infrequently reported in the context of systemic disease. Isolated colonic leukocytoclastic vasculitis without extraintestinal manifestations is rare. A previously unreported case of localized leukocytoclastic vasculitis of the left colon resulting in the impressive presentation of megacolon, without the presence of any precipitating factor or associated systemic disease is presented here, with an overview of the related literature.