This paper details a case study of a 4 month old Labrador Retriever mixed breed dog with Multiple Cartilaginous Exostoses (MCE). The puppy initially presented to the referring veterinarian for right forelimb lameness, and a large thoracic mass originating from the medial surface of a rib was unexpectedly found on radiographs. The dog was referred to Cornell University Hospital for Animals for further evaluation. Investigation revealed multiple, additional, non-aggressive, polyostotic proliferations of bone and cartilage throughout the puppy’s skeleton. The lesions, ranging from 1cm to 9 cm in diameter, were present on his limbs, ribs, vertebrae, within his vertebral canal, and on his pelvis. Although the genetic, autosomal dominant disease is benign, the dysplastic, proliferative masses grow rapidly until the animal reaches physical maturity. MCE is a self limiting disease except when the masses disrupt vital structures, and in this patient, the lesions were compressing his lungs causing clinical deficits. Because of the extensiveness and severity of the lesions, the puppy was not an ideal candidate for surgery. He was humanely euthanized and his body was donated for teaching purposes.