During the 11 months beginning in January, 1980, 22 cases of perinatal Listeria monocytogenes infection occurred at three obstetric hospitals in Auckland, New Zealand. Most cases were due to type 1b strains. Since the previous epidemic here in 1969, about one perinatal infection has been diagnosed annually in the same area. Women presented in preterm (11 of 22 cases) or term labor with signs of amnionitis (11 of 22 cases) and associated fetal distress and/or meconium-stained liquor (14 of 19 cases). A mild "flu"-like illness or urinary tract symptoms were common (18 of 22 women). Five fetal deaths occurred. Three were before 20 weeks of gestation. Most liveborn affected babies had early respiratory symptoms (12 of 14 cases). Meningitis occurred in 4 of 14 infants. There was one death. Vaginal carriage of L. monocytogenes was found in only 1 of 750 consecutive asymptomatic pregnant women who were tested at the time of the epidemic. Rectal carriage was found in 25 (3.3%). Pacific Island Polynesians were rectal carriers of L. monocytogenes and were represented among the epidemic cases more often than expected according to birth data (P less than 0.05 and P less than 0.001, respectively). The cause of the epidemic was not discovered but shellfish and raw fish consumption may have played a part.