Dogs may be infected with Mycobacterium tuberculosis, M bovis, and occasionally with M avium complex or M fortuitum, commonly from a human or bovine source. Tuberculous lesions are usually found in the lungs, liver, kidney, pleura, and peritoneum; they have a gray appearance, usually with a noncalcified, necrotic center. Lesions are often exudative and can produce a large quantity of straw-colored fluid in the thorax. False-negative tuberculin tests are often seen in dogs. Radiographs and a thorough history are useful in diagnosis. Treatment is not often recommended. Affected dogs in close contact with people should be euthanized because of public health concerns.