To determine whether the risk of sudden infant death syndrome (SIDS) among infants exposed to cocaine in utero may be elevated, we assessed the risk for SIDS in a large, well-described, prospective cohort of infants whose mothers had or had not used cocaine during pregnancy. Of 996 women consecutively enrolled while registering for prenatal care, 175 used cocaine during pregnancy. Only one infant of the mothers who used cocaine died of SIDS, a risk of 5.6 in 1000, compared with four infants among the 821 nonexposed infants, a risk of 4.9 in 1000. The relative risk for SIDS among infants whose mothers used cocaine during pregnancy compared with those whose mothers did not use cocaine was 1.17 (95% confidence interval 0.13, 10.43), suggesting that there is no increased risk of SIDS among infants exposed in utero to cocaine.