Mycobacterium tuberculosis infection in dogs is rarely reported and has not previously been documented in South Africa. A case of a stray Maltese crossbreed dog with extensive multifocal pulmonary tuberculosis due to M. tuberculosis is described. Pulmonary granulomas in this case were poorly encapsulated and contained large numbers of acid-fast bacteria, highlighting the potential for infected companion animals to excrete the pathogen. Treatment of canine tuberculosis is generally not advised, and for this reason, euthanasia of diseased animals must be advocated in most instances. Physicians and veterinarians must be aware that companion animals with active disease caused by M. tuberculosis could act as a potential source of infection.