Between 1975 and 1980, necropsy investigations were conducted on 44 wild koalas (24 males, 20 females) from several localities in Victoria, Australia. An additional 11 (5 males, 6 females) were presented for clinical appraisal and treatment. Traumatic injuries resulting from motor vehicle accidents and intra-specific conflict were the commonest reason for submission (19 of 55; 35%). Keratoconjunctivitis (8 of 55; 15%), ascending urinary tract infections (6 of 20 females; 30%), ascending genital tract inflammation (10 of 20 females; 50%) and sarcoptic mange (2 of 55; 4%) were recognized as specific diseases or disease syndromes. A peracute syndrome characterized by lassitude, depression, anorexia and coma was identified in moribund koalas submitted from the wild and also in hospitalized animals. The condition, termed koala stress syndrome, was thought to be initiated by intercurrent disease or trauma, long term hospitalization and frequent manipulation and treatments. Hematological observations in 54 apparently healthy wild koalas from five different populations and on 17 sick or injured animals are also presented. Certain blood parameters are discussed in relation to the health status of the populations or individuals. Areas for further research into koala diseases are also discussed.