Most infant deaths are certified by medical examiners or coroners. Statistical information from death certificates is consolidated into a national database through the National Vital Statistics System.1 Information on U.S. resident infant homicide deaths for 1989-1998 was obtained from CDC's National Center for Health Statistics. An infant was defined as a person aged <1 year at death. Homicide was defined as an underlying cause coded through the International Classification of Disease, Ninth Revision, codes E960–E969.3 Age at death in days was defined as one plus the difference between the dates of death and birth recorded on the death certificate. An infant killed on its date of birth had an age at death of 1 day. In comparison, homicide rates during different time periods within infancy were presented as rates per person-years of exposure. The U.S. infant population during 1989-1998 accounted for 39,941,628 person years of exposure, of which days of birth accounted for 109,354 person years, and the remainder of infancy accounted for 39,832,274 person years.