The first case of tuberculosis is described in a wild subantarctic fur seal (Arctocephalus tropicalis) found on the Argentine coast. There was hydrothorax and white firm granulomatous lesions of 40–50 mm in diameter in the lungs. Lesions consisted of a central area of caseous necrosis, an intermediate zone of epithelioid and lymphocytic mononuclear cells, and a peripheral zone of connective tissue. Biochemical and drug sensitivity tests and inoculation of Guinea pigs confirmed the identification as Mycobacterium tuberculosis complex. Arctocephalus tropicalis is the fifth pinniped species in which the M. tuberculosis complex has been detected. Since subantarctic fur seals are widely distributed in the Southern Hemisphere, it is possible that the tuberculosis cases may have a common origin and could spread to other austral regions and species.