Neonatal listeriosis, a condition associated with high morbidity and mortality, has been reported infrequently in Australia, with only seven isolated cases appearing in the literature. This paper describes 12 cases of neonatal listeriosis diagnosed in two Western Australian hospitals in the 22 months after January, 1978. These were the only cases diagnosed at these hospitals between 1970 and December, 1980. The early onset form of the disease was diagnosed in 11 infants, a group characterized by the frequent associations of low birthweight (mean, 1805 g; range, 1200 g to 2670 g), preterm delivery (gestational age: mean, 33 weeks; range, 28 weeks to 38 weeks), maternal fever at the onset of labour, meconium-stained liquor, low Apgar scores, respiratory distress and septicaemia. The delayed-onset form was diagnosed in one full-term infant (birth-weight, 3050 g) with probable meningitis at one week of age. The over-all mortality rate of 17% was low, perhaps as a result of the early institution of treatment and prompt transfer to a neonatal intensive care unit. Ten of the 12 cases presented during the hottest, driest period of the year. No other common epidemiological factor was identified.