A seven-year-old dead pet ferret (Mustela putorius furo) was brought to the National Veterinary Research Institute, Department of Microbiology, to have the disease diagnosed and cause of death determined. Significant loss of fur and various numerous skin lesions—such as nodules, bruises and small scabs— were found. A prominent subcutaneous cyst filled with semiliquid mass was observed on the right hindlimb, and the left eyelid was slightly swollen left eyelid with symptoms of conjunctivitis. On the basis of combined findings, the authors concluded that the ferret’s death was caused by a generalized Mycobacterium aviumsubspecies avium infection. Some immunodeficiency resulting from ferret’s age could be a predisposing factor. A feral cat, which was the only animal the ferret had contacted several weeks before the appearance of the first clinical symptoms, was a possible source of infection.