An approximately twelve year-old male captive killer whale developed bilateral axillary skin lesions which progressed from raised flat or smooth plaques to raised firm verrucoid lesions containing many fine anastomosing fissures. The lesions were pigmented either white or black in correspondence with the underlying skin and ultimately extended to the lateral thorax and peduncular tail stalk. Histologically, the lesions were characterized by marked epidermal hyperplasia with pronounced stratum intermedium keratinocyte cytoplasmic vesiculation. Multifocal epidermal necrosis with neutrophilic infiltrates and coccoid bacterial colonies were also present. The superficial dermis had a mild Lymphoplasmacytic perivascular dermatitis. Electron microscopic evaluation of the lesions demonstrated keratinocyte karyomegaly with peripherally redistributed chromatin. The nucleoplasm contained viral plaques made up of smaller spherical particles which sometimes formed para crystalline arrays and had an approximate diameter of 50-55 nm. The pathologic findings were consistent with a diagnosis of cutaneous papovaviral-like papillomatosis. Studies are ongoing to characterize this newly described viral disease and further investigate the immunologic status of the whale whose previous tests had suggested a disturbance in its cellular immunity.