Mycobacterium ulcerans infections were found in 11 koalas (Phascolarctos cinereus) between 1980 and 1985, in a population of approximately 200 koalas on Raymond Island in southeastern Australia. Ulcers caused by the infection occurred on the face, forearm, rump, groin and footpads. Seven koalas had multiple ulcers. All the infected animals were mature (age classes 4, 5 and 6), and eight were male. The distribution of ulcers corresponded with the distribution of wounds in a sample of 87 koalas. Many of these wounds were associated with social behaviour.