A 17-month-old male Labrador retriever presented for evaluation of an abdominal mass felt during abdominal palpation. Multiple variably sized cystic masses were identified on sonographic and radiographic images. Exploratory laparotomy revealed multiple peritoneal masses that exhibited atypical contractions and lacked an identifiable organ of origin. Histology and immunohistochemistry of multiple surgically excised masses was consistent with benign tumors of smooth muscle origin (leiomyomas). The presence of multiple peritoneal leiomyomas in this dog is consistent with disseminated peritoneal leiomyomatosis. Two years after diagnosis and multiple surgical interventions, continual insidious enlargement of leiomyomas was identified on ultrasound and CT.