Recently, considerable data have suggested that lipoprotein (a) [Lp(a)] is a strong independent risk factor for coronary heart disease. Since Lp(a) is increased in both insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM), this study examined the relationship of Lp(a) concentrations to coronary heart disease (CHD) mortality in the 4-year follow-up of the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR). Twenty-four older-onset subjects and 11 younger-onset subjects who died of CHD (cases) before the age of 70 were matched by age, gender, and type of diabetes to subjects who remained alive (controls). The distribution and mean levels of Lp(a) in the cases and controls were very similar, suggesting a lack of association between Lp(a) concentrations and CHD mortality. Although the number of subjects was small, caution should be used in extrapolating results on Lp(a) relationships in nondiabetic subjects to diabetic subjects.