During a 15 mo. period, all 34 infants delivered at the department of obstetrics and gynecology at University Hospital in Lund, Sweden, who died perinatally or neonatally, were included in a prospective study of causes of death. Autopsies (including extensive culturing of specimens for bacteria, Chlamydia, fungi, mycoplasmas and viruses) were performed for all infants. Maternal sera obtained during pregnancy and after delivery were examined regarding titers against a number of microorganisms. During the study period, the perinatal mortality rate was 0.60% and the neonatal mortality rate, 0.56%. Of the deaths, 37% were caused by lethal malformations, 17% by idiopathic respiratory distress syndrome and 9% by ablatio placentae. No less than 21% occurred as a direct consequence of infections, including 2 deaths caused by group B streptococci, 2 by coxsackievirus type B and 3 deaths each by Haemophilus influenzae, Pseudomonas aeruginosa and Candida albicans. A 6 mo. study of late abortions revealed another case of intrauterine group B streptococcal infection. Autopsy, including microbial examination, is recommended in all cases of perinatal and neonatal deaths.