Twenty-five patients with precocious coronary heart disease (CHD) (aged forty years or less) and 82 first-degree relatives were studied for lipid profile. Eighty-eight age- and sex-matched controls were also studied. The mean serum cholesterol, triglycerides, low density lipoprotein cholesterol, very low density lipoprotein cholesterol, and total cholesterol/high density lipoprotein cholesterol of patients and their first-degree relatives were significantly higher as compared with normal controls. High density lipoprotein cholesterol values were found to be almost identical in the patient group, their first-degree relatives, and normal controls. Hyperlipidemia was found in 68% of patients with CAD, of their first-degree relatives, and 24% of controls. Almost all lipid fractions in relatives of hyperlipidemic patients paralleled those of the patients suffering from CHD. Of 25 families studied, 16 had hyperlipidemia. In conclusion, it can be stated that there is a statistically significant hyperlipidemia in young patients with CHD that has a significant familial clustering, thus delineating a group of high-risk individuals (first-degree relatives of young coronary patients) for possible primary prevention of CHD. This familial clustering could be due to genetic or environmental factors; however, the relative contribution of these two factors requires further investigation.