Plasma lipoprotein(a) (Lp(a)) concentrations are associated with an increased risk of coronary artery disease in adults with familial hypercholesterolemia (FH). We hypothesized that Lp(a) concentrations in children with FH were higher among those with myocardial ischemia on stress thallium scans and among those with a family history of premature coronary artery disease. Twenty-nine asymptomatic heterozygotes with FH (range 9 to 23 years) and 7 homozygotes (range 4 to 13 years) were evaluated with clinical assessment, lipoprotein measurement and stress thallium scans. Compared with subjects with normal stress thallium scans, mean Lp(a) was significantly higher in homozygotes with stress thallium abnormalities (79 +/- 18 vs 15 +/- 5.5 mg/dl, p = 0.03), and tended to be higher in heterozygotes with stress thallium abnormalities (39 +/- 12 vs 20 +/- 4.2 mg/dl, p = 0.10). Lp(a) tended to be higher in heterozygotes with a family history of premature coronary artery disease (30 +/- 6.4 vs 14 +/- 4.1 mg/dl, p = 0.12). It is concluded that Lp(a) is higher in hypercholesterolemic children who have abnormal stress thallium scans. Lp(a) may be useful in assessing coronary artery disease risk in children with FH.