We studied 2962 cases of sudden infant death syndrome (SIDS), derived from linked birth and death records, to specify further the descriptive epidemiologic data on recognized SIDS risk factors and to examine interrelationships among multiple risk factors and SIDS while controlling for the influence of birth weight (using logistic regression). The results generally confirmed those of other studies, with the exception of a higher incidence of SIDS among Chinese and Japanese babies and a lower incidence among Hispanic babies, all in comparison with white, non-Spanish (Anglo) infants. Median age at death was found to vary by birth weight, with very low birth weight babies being about 6 weeks older (postnatal age) than normal birth weight babies at time of death. The association of the risk factors with SIDS remained when birth weight data were statistically controlled; the association of these risk factors with SIDS cannot be explained by their relationship to birth weight. An interaction was found between race and maternal age and between multiparity and type of hospital of birth. There was no interaction between birth weight and the other risk factors.