"Toby", an 8-year-old male, castrated mixed breed dog, presented to the Cornell University Companion Animal Hospital as an emergency on September 28, 1996, the chief complaint being anorexia, lethargy and recumbency. The initial physical examination performed at presentation revealed a recumbent dog, an abnormally slow heart rate (HR = 58 bpm) and a palpable abdominal mass located in the left upper abdominal quadrant. Subsequent labwork showed "Toby" to be hypercalcemic, with a serum calcium concentration of 15.4 mg/dl (N = 7.2-12.8 mg/dl). The main objectives of this paper are to present the differential diagnoses which must be considered in a hypercalcemic dog and how each differential causes an elevation in serum total calcium, to discuss the approach to the diagnostic workup of hypercalcemia in the small animal patient and to discuss the therapeutic options for the management of hypercalcemia. In addition, the normal physiology of calcium metabolism and homeostasis will be briefly discussed.