A 13-year-old castrated male Bassett Hound was examined because of a 2-week history of severe constipation and tenesmus. Radiography revealed a large cystic mass in the caudal portion of the abdomen that was compressing the urethra and obstructing the pelvic canal. A small perianal mass was also noticed in the region of the left anal sac. Exploratory surgery was performed, but the mass was deemed unresectable. Instead, the mass was incised, drained, and omentalized in an attempt to establish continuous drainage after surgery. Cytologic evaluation of the perianal mass was consistent with a diagnosis of anal sac adenocarcinoma. Histologic evaluation of the abdominal mass revealed it was a lymph node effaced by adenocarcinoma. Despite the poor prognosis for anal sac adenocarcinoma with metastatic spread to the sublumbar lymph nodes, tenesmus and dysuria in this dog remained palliated until the dog's death 18 months after surgery. Omentalization was successful in providing a continuous method of fluid drainage for this cystopapillary abdominal tumor.