A 4 mo old male goldendoodle puppy was evaluated for chronic hematochezia with a history of recurrent rectal prolapse and tenesmus. A colo-colonic intussusception was diagnosed via abdominal imaging. Surgery was elected to reduce the intussusception, wherein a colonic mass was discovered. Colonic resection and anastomosis was performed, and the tissue were submitted for histopathological examination. The puppy was diagnosed with colonic hamartomatous ganglioneuromatosis based on the presence of markedly hyperplastic submucosal and myenteric plexi with infiltration and expansion of the mucosa and submucosa by Schwann cells and neuronal cell bodies. Ganglioneuromatosis is a rarely reported entity in the veterinary literature, and limited clinical follow up data is available for described cases. In humans, ganglioneuromatosis is associated with a PTEN genetic mutation, which confers increased susceptibility to the development of neoplasia of endocrine organs. Approximately 1 yr after the operation, this puppy appeared clinically normal with no abnormalities on repeated imaging. This case report describes the clinical presentation, surgical treatment, and histologic features of colonic hamartomatous ganglioneuromatosis with 1 yr postoperative clinical follow up data in a dog. Although uncommon, ganglioneuromatosis should be considered as a differential diagnosis list as a cause of gastrointestinal masses in puppies and young dogs.