Multiple data sources were used to construct a database of intimate partner violence-related homicide cases from 1991 through 1995 in Massachusetts using an expanded case definition that includes others killed in the context of intimate partner disputes. Results show that nearly one in four victims who died in intimate partner-related incidents were victims other than the intimate partner. In a comparison of the FBI's Supplementary Homicide Report (SHR) with the study database, the SHR identified only 71.1% of the partner victims and could at best identify only 26.7% of the victims other than partners. Intimate homicides involving multiple victims were underreported in the SHR. Cases involving ex-boyfriend perpetrators were reported as partner homicides less often in the SHR than other intimate relationships. Rates calculated using a methodology designed to compensate for nonreporting and missing data in the SHR overestimated partner homicide rates. Issues of generalizability of these findings are discussed.