The study included 850,822 homicide-attributed deaths documented by the National Center for Health Statistics and incorporated graphical presentation, median polish, and Poisson regression modeling in an age-period-cohort analysis. Death rates from homicide in the United States doubled over the past four decades, with most of the increase occurring during the 1960's and early 1970's. Poisson regression models confirmed that the rise of homicide mortality in both men and women was largely attributable to a significant period effect between 1960 and 1974. No discernible cohort patterns were found among women. However, homicide rates for recent male birth cohorts appeared to peak at younger ages and at higher levels. A significant increase in homicide mortality risk beginning with males born around 1965 was found by examining the residuals of median polish and the second-order changes in regression coefficients from the age-period-cohort model. The increase in homicide mortality during 1985 and 1994 was explained by this cohort effect. The authors indicate the increased prevalence of substance abuse and the availability of firearms are two likely factors underlying the disturbing cohort pattern. 51 references, 3 tables, and 8 figures