A 7-year-old adult male ferret had progressive hair loss that was bilaterally symmetric. Also clinically evident were severe dehydration, polydipsia, muffled heart sounds, weak femoral pulses, hepatomegaly, lethargy, weakness, temporal muscular atrophy, dyspnea, and weakness. The blood profile of the ferret indicated profound leukopenia, eosinopenia, and high phosphorus, BUN, creatinine, and potassium concentrations, as well as high aspartate transaminase activity; the albumin concentration was low. The serum cortisol concentration was 8.1 micrograms/dl. Necropsy and histologic findings confirmed a diagnosis of hyperadrenocorticism, complicated by dilatative cardiomyopathy, chronic active hepatitis, and renal disease.