AbstractBACKGROUND: Completeness of case ascertainment is a concern for all birth defects registries and generally requires a multisource approach. Using infant death certificates as one case ascertainment source may identify cases of birth defects that would have otherwise been missed. We sought to examine the utility of adding infant death certificates to the Florida Birth Defect Registry's (FBDR) case ascertainment methods and to determine what factors are associated with the registry's failure to capture infants that die from birth defects. METHODS: FBDR cases from 1999 to 2006 were matched to a statewide linked birth‐infant death file. Descriptive statistics were used to assess the FBDR's ability to capture infants with a birth defect‐related cause of death (COD) and identify conditions most commonly missed. Factors associated with the FBDR's failure to capture an infant who died from a birth defect during the first year of life were identified with logistic regression models. RESULTS: There were 2558 (21.1%) infant deaths with birth defects listed as the underlying or an associated COD, of which the FBDR captured 73.3%. Most often missed defects included malformation of the coronary vessels, lung hypoplasia/dysplasia, anencephaly, and unspecified congenital malformations. Logistic regression identified gestational age/birth weight, age at death, autopsy decision, plurality, adequacy of prenatal care, and maternal nativity as factors associated with the FBDR's failure to capture an infant with a birth defect‐related COD. CONCLUSIONS: Although the overall potential contribution of infant death certificates to the FBDR is small, this source contributes to the prevalence of specific defects. Birth Defects Research (Part A), 2010. © 2010 Wiley‐Liss, Inc.