The Milwaukee County Zoo has housed common vampire bats (Desmodus rotundus) since 1973. The bats are fed defibrinated cow's blood supplemented with a liquid pediatric multivitamin. From July 2013 to May 2014, multiple deaths occurred in colony bats, including five juveniles with multiple bone fractures and failure of endochondral ossification, three adults with cerebellar necrosis, and one adult with subcutaneous hemorrhage. In November 2013, an adult bat developed a nonhealing left wing hematoma and eventually succumbed 9 mo later. A postmortem examination revealed multifocal extensive necrohemorrhagic and suppurative ulcerative dermatitis with no underlying cause determined. From July to December 2014, five of nine adult bats in the colony developed similar hematomas along with gingival bleeding. One euthanized bat had a serum ascorbic acid level of 0.08 mg/dl and marked generalized subcutaneous hemorrhage. A therapeutic trial was initiated in which two bats received defibrinated cow's blood supplemented only with oral vitamin C, 100 mg/kg PO q24h for 3 d, and then 50 mg/kg PO q24h. Two other bats received nonsupplemented defibrinated cow's blood and were given vitamin K 3.3 mg/kg SC q12h for 3 d, and then 3.3 mg/kg SC q24h for 7 d. The bats supplemented with vitamin C improved, supporting a diagnosis of vitamin C deficiency. All bats were subsequently supplemented with vitamin C leading to resolution of all lesions within 10 d to 2 mo. Vitamin C is necessary for collagen synthesis, which is required for proper wound healing, capillary and cartilage strength, osteoid production, and pial membrane formation of the cerebellum. Several bat species cannot synthesize vitamin C and require a dietary source. This is the first report of vitamin C deficiency in a colony of vampire bats leading to severe chronic subcutaneous hemorrhage, bone fragility, microfractures, cerebellar necrosis, and death.