Biliary cystadenocarcinomas are a very rare set of neoplasms that occur in the liver, the extrahepatic bile duct system, and occasionally in the gallbladder. We report on a 75-year-old man with a cystadenocarcinoma of the gallbladder who presented with mild abdominal discomfort and a palpable mass in the right upper abdomen. The diagnostic workup included ultrasound, magnetic resonance tomography, and fine needle core biopsy and revealed a multicystic tumor 16 cm in diameter. The patient underwent multivisceral resection of the tumor with a resection of the right colon, a partial resection of the stomach and the liver, and a lymph node dissection. The resected specimen weighed 2500 g and the final histopatholical diagnosis was a primary, moderately differentiated cystadenocarcinoma of the gallbladder with two lymph node metastases and invasion of the right colon. The patient remains without evidence of recurrence 12 months after surgery. The clinical presentation, diagnosis, therapeutic options, and classification of hepatobiliary cystadenocarcinomas are discussed.