High-density (HD) lipoprotein cholesterol levels have been inversely associated with the incidence of coronary heart disease. The clinical features were reviewed and the prevalence of clinically evident coronary artery or other vascular disease was ascertained in 27 homozygous and 22 obligate heterozygous patients with familial HD lipoprotein deficiency (Tangier disease). Mean HD lipoprotein cholesterol levels were 4 mg/dL in homozygotes, 26 mg/dL in heterozygotes, and 54 mg/dL in normal subjects. Mean low-density (LD) lipoprotein cholesterol levels were 47 mg/dL in homozygotes, 120 mg/dL in heterozygotes, and 124 mg/dL in normal subjects. In heterozygotes or homozygotes 35 years of age or less no evidence of vascular disease was noted. In subjects between 35 and 65 years of age, five of 19 heterozygotes (26%) and five of 11 homozygotes (45%) had some evidence of coronary artery or cerebrovascular disease, as compared to 4% or less in a normal population. The data are consistent with the concept that patients with familial HD lipoprotein deficiency may be at increased risk for premature vascular disease. However, the strikingly accelerated atherosclerosis seen in patients with familial hypercholesterolemia is not seen in patients with Tangier disease possibly due to their normal or reduced LD lipoprotein cholesterol levels.