Although national level studies in the United States and Canada find that extreme partner age discrepancy is a risk factor for intimate partner homicide in opposite-sex couples, these studies carry two caveats: They are limited to cohabiting marital or common-law couples and they are not detailed enough to explore alternative explanations for the age discrepancy-homicide risk association. Using the Chicago Homicide Dataset, which includes all homicides that occurred in Chicago from 1965 to 1996, we analyze the 2,577 homicides in which the victim was killed by a current or former legal spouse, common-law spouse, or heterosexual boyfriend or girlfriend, and in which the woman was at least 18 years of age. Within each of 14 categories of couple age discrepancy, we estimate the population of intimate heterosexual couples and calculate the population-based risk of homicide. The results replicate national level findings showing that the risk of intimate partner homicide is considerably elevated for couples with a large discrepancy between their ages—where the man is at least 16 years older than the woman or the woman is at least 10 years older than the man. This risk pattern occurs regardless of whether the man or the woman was the homicide offender. We then investigate whether the link between partner age discrepancy and homicide risk is explained by the offender's arrest record. Results show that the higher risk of intimate partner homicide for age discrepant couples is robust, and does not depend on the previous arrest record of the offender. Discussion addresses other possible explanations for the increased risk of partner homicide for age discrepant couples, and the practical implications of these findings.