It remains uncertain whether established risk factors for coronary heart disease in middle-aged persons can be generalized to elderly persons. Based on a case-control study, risk factors for nonfatal acute myocardial infarction (AMI) were assessed separately in middle-aged (40-64 years) and older (65-79 years) Japanese. Eligible cases were patients who were admitted to 22 collaborating hospitals for the first AMI between September 1996 and January 1998. Community controls were recruited by using the resident registers of the municipalities with individual matching by gender, year of birth (within 2 years), and proximity in residence. The present study used 384 sets of 384 cases and 656 controls. Smoking, hypertension, and angina pectoris were associated with an increased risk of AMI, and alcohol use and leisure-time exercise were related to a decreased risk of AMI in the elderly as well as in middle-aged persons. There was no apparent relation between body mass index and AMI in either middle-aged or older adults. Diabetes mellitus was significantly associated with an increased risk of AMI in older persons, but not in middle aged persons. Hypercholesterolemia was related to an increased risk of AMI in middle-aged individuals alone. The findings suggest that risk factors for AMI in the elderly are generally similar to those of middle-aged persons, but provide no evidence that hypercholesterolemia in the elderly is an important risk factor.