Background-The extent to which the relative contributions of traditional cardiovascular risk factors to incident cardiovascular disease (CVD) may have changed over time remains unclear. Methods and Results-We studied 13 541 participants (56% women, 26% black) in the Atherosclerosis Risk in Communities Study, aged 52 to 66 years and free of CVD at exams in 1987 through 1989, 1990 through 1992, 1993 through 1995, or 1996 through 1998. At each examination, we estimated the population attributable risks (PAR) of traditional risk factors (hypertension, diabetes mellitus, obesity, hypercholesterolemia, and smoking) for the 10-year incidence of CVD. Overall, the PAR of all risk factors combined appeared to decrease from the late 1980s to the late 1990s (0.58 to 0.53). The combined PAR was higher in women than men in 1987 through 1989 (0.68 versus 0.51, P<0.001) but not by the late 1990s (0.58 versus 0.48, P=0.08). The combined PAR was higher in blacks than whites in the late 1980s (0.67 versus 0.57, P=0.049), and this difference was more pronounced by the late 1990s (0.67 versus 0.48, P=0.002). By the late 1990s, the PAR of hypertension had become higher in women than men (P=0.02) and also appeared higher in blacks than whites (P=0.08). By the late 1990s, the PAR of diabetes mellitus remained higher in women than men (P<0.0001) and in blacks than whites (P<0.0001). Conclusions-The contribution to CVD of all traditional risk factors combined is greater in blacks than whites, and this difference may be increasing. The contributions of hypertension and diabetes mellitus remain especially high, in women as well as blacks. These findings underscore the continued need for individual as well as population approaches to CVD risk factor modification.