Brainstem gliosis is elevated in some SIDS victims and has been associated with hypoxic-ischaemic events. Factors which increase the risk of SIDS include possible risk factors for hypoxic-ischaemic events during foetal and perinatal life. In this study a scoring system was developed whereby possible risk factors for hypoxic-ischaemic events during pregnancy, birth and in the perinatal period were correlated with the level of gliosis in the nucleus olivaris inferior in SIDS victims (n = 19). The mothers' antenatal care and obstetric records and the SIDS infants' perinatal hospital records were investigated, and each possible risk factor for hypoxic-ischaemic events was given one point. The points were summarized for each infant, and this sum was correlated with the level of gliosis in the infant's nucleus olivaris inferior. The number of cigarettes the mothers smoked during pregnancy was also compared with the level of gliosis. Our results show that in SIDS victims there is 41% probability that the more the mothers smoked during pregnancy, the more gliosis in the nucleus olivaris inferior is found in their infants (p < 0.01). Gliosis in the nucleus olivaris inferior also correlated with the possible risk factors for hypoxic-ischaemic events during pregnancy, birth and the perinatal period (r2 = 0.28, p < 0.05). However, if cigarette smoking was excluded as a possible hypoxic-ischaemic risk factor, no correlation was found.