Magnesium (Mg) deficiency is believed to have adverse cardiovascular consequences that are broad and complex, although an association between dietary Mg intake and the risk of coronary heart disease (CHD) has not been clearly identified. The purpose of this study is to examine the relation between dietary Mg intake and future risk of CHD. Reported findings are based on dietary Mg intake in 7,172 men in the Honolulu Heart Program. Intake of Mg was recorded at baseline examinations that took place from 1965 to 1968 when the men were aged 45 to 68 years. In 30 years of follow-up, 1,431 incident cases of CHD were identified. Within 15 years after dietary assessment, the age-adjusted incidence decreased significantly from 7.3 to 4.0 per 1,000 person-years in the lowest (50.3 to 186 mg/day) versus highest (340 to 1,183 mg/day) quintiles of Mg intake (p <0.001). When adjustments were made for age and other nutrients (singly or combined), there was a 1.7- to 2.1-fold excess in the risk of CHD in the lowest versus highest quintiles (p <0.001). The excess risk ranged from 1.5- to 1.8-fold after further adjustment for other cardiovascular risk factors (p <0.05). Associations between dietary Mg and coronary events occurring after 15 years of follow-up were modest. We conclude that the intake of dietary Mg is associated with a reduced risk of CHD. Whether increases in dietary Mg intake can alter the future risk of disease warrants further study.