This report presents three cases of mycobacteriosis in gang gang cockatoos (Callocephalon fimbriatum) that highlight the potential variation in clinical presentation of this important avian disease. The first case was a female gang gang cockatoo with widespread skeletal disease that presented with a chronic history of weight loss and nonpainful, bilaterally symmetric, distal-wing and leg nodular swellings. The second case was a mature female in good muscle condition with a nodular granulomatous pericarditis and myocarditis causing severe hydropericardium and cardiac tamponade; it was presented for respiratory distress. The third case was one of alimentary mycobacteriosis that presented with a chronic history of weight loss. Some difficulties associated with confirming a premortem diagnosis of mycobacteriosis are discussed.