Description: Medical records of six dogs admitted with acute hypoadrenocorticism were reviewed. All 6 animals were bradycardic and had prolonged capillary refilling time. Hypothermia was detected in 5/6 animals. Clinicopathological evaluation on admission revealed anemia (3/6 dogs), increased (2/6) and normal (2/6) lymphocyte and eosinophil counts, azotemia and hyperkalemia (6/6), hyponatremia, in 5/6 dogs in which sodium was measured with a sodium (Na) : potassium (K) ratio lower than 24, hypoglycemia (2/6) and hypercalcemia, hypocholosterolemia, increased serum alkaline phosphatase and alaninoaminotransferase activities, one dog each. Urine specific gravity was lower than 1025 in 4 dogs. Thoracic radiographs and abdominal ultrasonography disclosed microcardia (2/6), pleural effusion (2/6) and ascites (1/6). Two dogs (2/6), also, presented atrial standstill or atrioventricular block, detected on electrocardiograms. In all 6 animals emergency treatment included the use of intravenous normal saline and glucocorticoids (dexamethasone) immediately after the completion of an ACTH stimulation test with tetracosactide. Two dogs died, one during the 1 st day and the other on the 4th day of hospitalization, the latter after the sudden appearance of severe hemorrhagic gastroenteritis. Hospitalization time in the remaining 4 dogs ranged from 3 to 10 days. Prolongation of hospitalization was associated with worsening of anemia, hypoalbuminemia, neurologic complications and non-responsive azotemia. Four dogs (4/6) were discharged on oral prednisolone and fluodrocortisone, but one died after a week for unknown reasons. Acute hypoadrenocorticism is a life-threatening condition requiring emergency treatment for a successful outcome. Its inclusion in the differential diagnosis of canine emergencies, presented with acute weakness and gastrointestinal signs, is mandatory, but for its confirmation a complete laboratory and, most importantly, an ACTH stimulation test are always required