Seventy heterozygous patients with familial hypercholesterolemia (FH), aged 3 to 91 years (37 men and 33 women), from 38 different families were studied to ascertain their clinical profiles including the pattern of distribution of total cholesterol (TC), Achilles tendon thickness (ATT), and a sex difference in age at the onset of ischemic heart disease (IHD). Eighteen family members who died of IHD were included in this study. The TC level was 332.2 +/- 95.0 mg/dl (mean +/- SD), and the ATT was 12.0 +/- 2.7 mm. IHD was observed in 20 men and 8 women, with an incidence in men 2.5 times higher than that in women. The mean age at the onset of IHD in men was in the sixth decade, one decade younger than in women. IHD was even observed in patients with TC levels of nearly 230 mg/dl. One of the 18 family members was considered a homozygote of the disease by autopsy findings. Twelve of the remaining members died suddenly, and another five had fatal myocardial infarction. We conclude that, (1) IHD is frequently associated with FH, even though TC levels are 230-300 mg/dl, (2) complications of IHD peak earlier in men (sixth decade) than in women (seventh decade) and (3) relatively large numbers of family members died suddenly, especially men.