As part of the Caerphilly and the Speedwell collaborative heart disease studies, associations between outdoor traffic noise level, risk factors for ischemic heart disease, and prevalence and incidence of ischemic heart disease were studied in two samples of 2,512 and 2,348 men, respectively, who were 45-63 y of age. Compared with the lowest noise category [Leq,6-22 h = 51-55 dB(A)], the subjects in the highest noise category [Leq,6-22 = 66-70 dB(A)] showed a slightly worse risk factor profile with respect to 9 identified endogenous risk factors. Logistic regression analysis suggested a marginal increase in risk (relative risk = 1.1) for ischemic heart disease incidence for these men based on risk factors. The prevalence of ischemic heart disease was slightly higher (relative risk = 1.2) in this noise group. The observed incidence of major ischemic heart disease within an observation period of approximately 4 y was slightly lower (relative risk = 0.8) for men in the highest noise group.