BACKGROUND AND OBJECTIVES: The purpose of this study was to investigate the familial correlation and heritability of the LDL cholesterol level through a segregation analysis. SUBJECTS AND METHODS: This study was based on the data from 9,884 Korean individuals, ascertained as pedigrees, who had participated in the 1998 and 2001 Korean National Health & Nutrition Examination Survey. The subjects of the segregation analysis were 3,613 Korean with more than five family members. RESULTS: The LDL cholesterol level revealed a strong familial correlation among spouses, parental-offspring and siblings; a low correlation with spouses, but a high correlation with parental-offspring and siblings. The heritability of the LDL cholesterol level was 37.3%, when controlled for age, age2, gender, age x gender, waist circumference, smoking, alcohol drinking, exercise and education. After the segregation analysis, models of the major gene effects were rejected in the general population. However, the Mendelian dominant and co-dominant models were found in high risk families. CONCLUSION: In conclusion, the randomly ascertained Korean families of this study showed strong familial aggregation in the LDL cholesterol level. This suggested that variations in the level of LDL cholesterol may be influenced by a major gene effect.