During a 3-year-period, hypercalcemia was found in 16 (28%) of 62 dogs with hypoadrenocorticism. Thirteen of the dogs were hypercalcemic at the time of diagnosis, whereas hypercalcemia developed at relapse during maintenance corticosteroid therapy in 3 dogs. The severity of hypercalcemia correlated with the severity of hypoadrenocorticism. Clinical signs and biochemical disturbances were more severe and mean calcium concentration was significantly higher in the dogs that were hypercalcemic at time of diagnosis than in the dogs that became hypercalcemic while on therapy. In all dogs, the high calcium concentration promptly and completely resolved with adequate corticosteroid replacement therapy.