This case report describes a 10-year-old female spayed, Domestic Shorthair cat that was diagnosed with an intestinal mast cell tumor (MCT). This report will highlight feline mast cell disease, with specific emphasis on intestinal mast cell tumors in cats. Current diagnostic techniques and treatments will be discussed. The cat presented with a four to five weekhistory of constipation, and a more recent one day hist01y of inappetance, lethargy, and vomiting. Physical exam revealed a painful abdomen with a descending colon full of firm, hard feces, and a palpable band of tissue located around the distal colon. A colonic mass was highly suspected at that time. Bloodwork revealed an inflammatory leukogram with band neutrophils and mild to moderate toxic change. An abdominal ultrasound was performed, which revealed a 3.2cm by 2.8cm by 1.9cm transmural, circumferential mass in the distal colon. An enlarged colonic lymph node (1.4cm), nodules present in the spleen (3-4mm), and a scant amount of peritoneal fluid were also detected on abdominal ultrasound. A fine needle aspirate was taken of the mass, and cytology diagnosed the mass as a mast cell tumor with septic suppurative inflammation and fibroplasia. Due to high likelihood of metastasis and poor prognosis, owners elected euthanasia for the cat.