OBJECTIVE: Approximately 2000 children die annually in the United States from maltreatment. Although maternal and child risk factors for child abuse have been identified, the role of household composition has not been well-established. Our objective was to evaluate household composition as a risk factor for fatal child maltreatment. METHODOLOGY: Population-based, case-control study using data from the Missouri Child Fatality Review Panel system, 1992-1994. Households were categorized based on adult residents' relationship to the deceased child. Cases were all maltreatment injury deaths among children <5 years old. Controls were randomly selected from natural-cause deaths during the same period and frequency-matched to cases on age. The main outcome measure was maltreatment death. RESULTS: Children residing in households with adults unrelated to them were 8 times more likely to die of maltreatment than children in households with 2 biological parents (adjusted odds ratio [aOR]: 8.8; 95% confidence interval [CI]: 3.6-21.5). Risk of maltreatment death also was elevated for children residing with step, foster, or adoptive parents (aOR: 4.7; 95% CI: 1.6-12.0), and in households with other adult relatives present (aOR: 2.2; 95% CI: 1.1-4.5). Risk of maltreatment death was not increased for children living with only 1 biological parent (aOR: 1.1; 95% CI: 0.8-2.0). CONCLUSIONS: Children living in households with 1 or more male adults that are not related to them are at increased risk for maltreatment injury death. This risk is not elevated for children living with a single parent, as long as no other adults live in the home.