The significantly higher incidence of both sickle cell trait (SCT) and sudden infant death syndrome (SIDS) in the black population suggests that SCT and SIDS may be epidemiologically related. To study this possibility, we identified, for the period of February 1990 to February 1992, all infants with SCT born in Los Angeles County whose disease was diagnosed through the California Newborn Screening Program. We matched these infants with all confirmed cases of SIDS in Los Angeles County from February 1990 to March 1993. Three cases of SCT among 589 infants confirmed to have had SIDS were identified. The incidence of SIDS was 1.25/1000 live births for the general population versus 0.58/1000 cases for the SCT group. This finding remained unchanged when rates were adjusted for ethnicity. We conclude that infants born with SCT are not at increased risk of dying of SIDS.