Primary hypoadrenocorticism, or Addison's disease, is an uncommon endocrine disease that is believed to result from immune-mediated destruction of the adrenal cortices. All layers of the adrenal cortex are typically affected, resulting in glucocorticoid, mineralocorticoid, and sex hormone deficiency. The history and clinical signs are usually vague, nonspecific, and often wax and wane. Clinical pathology often reveals electrolyte abnormalities resulting from the lack of aldosterone. Definitive diagnosis is achieved with the adrenocorticotrophic hormone (ACTH) stimulation test. Therapy involves replacing the deficient mineralocorticoids and glucocorticoids. Addison's disease can be well controlled with medication, and the prognosis for most dogs is good to excellent. In the following case discussion, many of the patient's clinical signs and bloodwork abnormalities were consistent with hypoadrenocorticism; however, other aspects of the clinical presentation made the diagnosis more difficult.