Previous studies by our group and others suggest that infants born to Mexican (MX) and Puerto Rican (PR) mothers may have lower risks of death due to SIDS. The reason(s) for this protective effect remain unexplained. Overall MX infants have about the same level and PR infants have higher levels of mortality than Non-Hispanic Whites (NHW). We investigated whether the lower risk of death due to SIDS among MX and PR infants could be due to their higher rates of other/competing causes of infant death. Using a 50% random sample of the U.S. linked infant birth and death data for the year 1990 (N = 1,842,681), we estimated Cox proportional hazard models of SIDS which had been modified to account for the competing risks of ten other causes of infant death. In addition to maternal race, the adjusted models included birth weight as well as maternal age, education, marital status, parity, interpregnancy interval, birth order, prenatal care, tobacco and alcohol use. Results showed that the crude hazard of infant death due to all causes combined was essentially identical between NHW and MX [Crude Hazard Ratio (HR): 1.04, p=0.19] but about 40% higher for PR [Crude HR: 1.39, p < 0.001]. The adjusted hazards of all cause mortality were about 20% lower for both MX [Adjusted HR: 0.82, p < 0.0001] and PR [0.79, p=0.0004] as compared with NHW. In contrast, both the crude and the adjusted SIDS-specific hazard rates were substantially lower for MX [Crude SIDS-specific HR: 0.67, p < 0.0001 - Adjusted SIDS-specific HR: 0.40, p < 0.0001] and for PR [Crude SIDS-specific HR: 0.63, p < 0.0001 - Adjusted SIDS-specific HR: 0.33, p < 0.0001]. Conclusions: 1) The lower risk of SIDS in infants born to Mexican and Puerto Rican mothers is not due to higher risks of mortality due to other/competing causes of infant death. 2) The mechanism(s) for the protective effect of Mexican/Puerto Rican ethnicity on the risk of SIDS such as differences in sleeping habits among Mexican and Puerto Rican families need further study.