Introduction: Sugar gliders (Petaurus breviceps) have grown in popularity as a zoological companion animal species. Thus, this species may be presented to veterinarians for a variety of medical conditions. Little is known about this species, especially the causes of their mortality in captivity. The objective of this study was to describe the causes of mortality of sugar gliders presented to a veterinary teaching hospital in Colorado, United States. Materials and Methods: A medical record database was searched from April 7, 2000 through January 24, 2023. Records from 68 sugar gliders were evaluated. Inclusion criteria were sugar gliders that had presented to the veterinary teaching hospital that had a complete necropsy performed, including histopathology. Results: Data were included from 68 sugar gliders, with 24 males, 13 females, and 31 unknown sexes. Ages at postmortem ranged from 2.85 months to 13.25 years old. The most common causes of mortality included nephritis (13/68, 19%), enteritis and/or colitis (11/68, 16%), and hepatitis (10/68, 15%). Lymphoplasmacytic changes were found in 44/68 individuals. Other causes included respiratory and neurological disease. Discussion: These results showed that stress-induced anorexia combined with systemic inflammation and infection was the leading cause of death. This may be related to suboptimal husbandry and diet in captivity. Future work should focus on increasing data through incorporating multiple institutions across the country. Conclusions: Establishing the leading causes of mortality aids in expanding the knowledge of sugar gliders as pets and may lead to prevention and treatment options that increase their survivability in captivity.