Abscesses of the thigh are rare and, although easily diagnosed, their cause is often obscure. We present two cases of thigh abscesses which resulted from the extension of intraabdominal sepsis. A review of the literature reveals only 46 previously reported cases. The underlying pathologic abnormality is usually a retroperitoneal perforation of a colorectal neoplasm or diverticular disease, whereas origin from the small bowel or appendix is distinctly less common. Routes of extension of infection into the thigh can be either direct, through the subcutaneous tissues, or through naturally occurring defects in the abdominal wall. These include: (1) along the psoas muscle deep to the inguinal ligament; (2) through the femoral canal; (3) by way of the obturator foramen; and (4) through the sacrosciatic notch. The two cases presented are unusual in that they both followed radical cystectomy with lymph node dissection, which opens up these natural avenues to the spread of intraabdominal infection. The overall mortality in the literature is high (53 percent), but recognition of an abdominal source and appropriate treatment combined with local drainage of the thigh abscess appears to improve survival.