OBJECTIVE:To determine whether maternal or paternal use of cocaine, opiates, or marijuana during conception and pregnancy and postnatally increases the risk of sudden infant death syndrome (SIDS) during the first year of the infant's life. This is an important issue and may prove useful in further decreasing the rate of SIDS. METHODS:A case-control study was conducted consisting of 239 infants who died of SIDS in southern California between 1989 and 1992, and 239 healthy infants who were matched on the basis of birth hospital, date of birth, age, and sex. Specific drug use at the period of conception, during pregnancy and breastfeeding, and in the presence or vicinity of the infant was ascertained by telephone for the white, African American, Hispanic, Asian American, and Pacific Islander case and control fathers and mothers. RESULTS:Maternal recreational drug use during pregnancy was not associated with the risk of SIDS after adjusting for maternal smoking during pregnancy (adjusted odds ratio [OR] = 2.0; 95% confidence interval [CI], 0.6-6.5). There were statistically significant differences between case and control fathers' use of marijuana during conception (OR = 2.2; 95% CI, 1.2-4.2; P =.01), during pregnancy (OR = 2.0; 95% CI, 1.0-4.1; P =.05), and postnatally (OR = 2.8; 95% CI, 1.1-7.3; P =.04) and the risk of SIDS, while adjusting for paternal smoking and alcohol use. CONCLUSIONS:There was no association between maternal recreational drug use and SIDS. Paternal marijuana use during the periods of conception and pregnancy and postnatally were significantly associated with SIDS. The role of paternal psychoactive drug use, especially the relationship between marijuana and SIDS, is an understudied area; however, before any definitive role for the father can be confirmed, these findings should be investigated and replicated in future studies.