The independent contributions of baseline major and minor electrocardiographic (ECG) abnormalities to subsequent 11.5 year risk of death from coronary heart disease, all cardiovascular diseases and all causes were explored among 9,643 white men and 7,990 white women aged 40 to 64 years without definite prior coronary heart disease in the Chicago Heart Association Detection Project in Industry. At baseline, prevalence rates of major ECG abnormalities were higher in women than in men, with age-adjusted rates of 12.9 and 9.6% (p less than 0.01), respectively. Minor ECG abnormalities were more common in men than in women (7.3 versus 4.5%, p less than 0.01). Both major and minor ECG abnormalities were associated with an increased risk of death from coronary heart disease, all cardiovascular diseases and all causes. The strength of these associations was greater in men than in women. When baseline age, diastolic pressure, serum cholesterol, cigarettes smoked per day, diabetes and use of antihypertensive medication were taken into account, major abnormalities continued to be significantly related to each cause of death in both genders with much larger adjusted absolute excess risk and relative risk for men than for women. In multivariate analyses, minor ECG abnormalities contributed independently to risk of death in men, but not clearly so in women. The results indicate the independent association between ECG abnormalities and mortality from coronary heart disease, all cardiovascular diseases and all causes, with greater relative significance in middle-aged United States men than women.