OBJECTIVE To compare lipoprotein(a) levels in diabetic patients and normoglycemic relatives in familial NIDDM and to assess whether Lp(a) is a risk factor for myocardial infarction in this population. RESEARCH DESIGN AND METHODS We compared 577 patients and 261 normoglycemic relatives from 189 NIDDM multiplex families with 49 unrelated healthy individuals. of the 577, 23 patients with previously documented myocardial infarction were further analyzed as a separate group. RESULTS Lp(a) concentrations in diabetic patients, normoglycemic relatives, and the control group were not significantly different. Variance of Lp(a) in a given individual could not be accounted for by any clinical or biological parameter, but was strongly related to the mean Lp(a) value in his or her family. Diabetic patients with previous myocardial infarction (and their relatives) had significantly higher levels of Lp(a) than patients without coronary heart disease complaints. CONCLUSIONS Lp(a) concentration in familial NIDDM was not related to the degree of glucose intolerance, but presented a strong familial aggregation. High Lp(a) levels seem to be an independent risk factor for myocardial infarction in this NIDDM cohort.