Carcinosarcoma of the gallbladder is a rare malignancy characterized by both malignant epithelial and mesenchymal components. The clinical behavior of this tumor is extremely aggressive. Only 26 cases have been reported in the world literature to date. We report the case of a 64-year-old woman who had fever associated with a right upper quadrant mass. An exploratory laparotomy through a right upper quadrant incision was performed at another institution, and the patient was thought to have severe acute cholecystitis that would require additional antibiotic therapy before attempted resection. She was referred to our center, where abdominal CT showed a 6.4 x 8.2 cm pericholecystic mass involving the hepatic flexure of the colon. The patient underwent cholecystectomy and hepatic wedge resection, pancreaticoduodenectomy, and right hemicolectomy. Pathologic examination of the surgical specimen revealed two histologic components consisting of squamous cell carcinoma and spindle cell sarcoma of gallbladder origin, consistent with carcinosarcoma. All seven lymph nodes in the pancreaticoduodenectomy specimen were negative for tumor. We present this case and a review of the literature and current treatment recommendations.