ABSTRACT. Objective. To determine the role of household composition as an independent risk factor for fatal inflicted injuries among young children and describe perpetrator characteristics.Design, Setting, and Population. A population-based, case-control study of all children <5 years of age who died in Missouri between January 1, 1992, and December 31, 1999. Missouri Child Fatality Review Program data were analyzed. Cases all involved children with injuries inflicted by a parent or caregiver. Two age-matched controls per case child were selected randomly from children who died of natural causes.Main Outcome Measure. Inflicted-injury death. Household composition of case and control children was compared by using multivariate logistic regression. We hypothesized that children residing in households with adults unrelated to them are at higher risk of inflicted-injury death than children residing in households with 2 biological parents.Results. We identified 149 inflicted-injury deaths in our population during the 8-year study period. Children residing in households with unrelated adults were nearly 50 times as likely to die of inflicted injuries than children residing with 2 biological parents (adjusted odds ratio: 47.6; 95% confidence interval: 10.4 -218). Children in households with a single parent and no other adults in residence had no increased risk of inflicted-injury death (adjusted odds ratio: 0.9; 95% confidence interval: 0.6 -1.9). Perpetrators were identified in 132 (88.6%) of the cases. The majority of known perpetrators were male (71.2%), and most were the child's father (34.9%) or the boyfriend of the child's mother (24.2%). In households with unrelated adults, most perpetrators (83.9%) were the unrelated adult household member, and only 2 (6.5%) perpetrators were the biological parent of the child.Conclusions. Young children who reside in households with unrelated adults are at exceptionally high risk for inflicted-injury death. Most perpetrators are male, and most are residents of the decedent child's household at the time of injury. Using vital-records data makes it possible to conduct large, population-based studies to identify risk factors for fatal inflicted injuries. It is well documented, however, that studies based on vital records severely underestimate child maltreatment deaths, with 50% to 85% of child maltreatment deaths misclassified as resulting from other causes. [3][4][5][6][7] In addition, vital-records data are typically limited to a small subset of maternal and child variables and provide no information on household composition, the perpetrators, or their relationship to the decedent child. This combination of pronounced misclassification and lack of risk-factor information in vital records severely limits the usefulness of these data for child-maltreatment research. 1,[8][9][10] Combining data from multiple sources, now a common practice in many state-based child-fatalityreview programs, can greatly reduce the misclassification of maltreatment fatalities as resulting from other c...