Background: High-density lipoprotein (HDL) is a major plasma lipoprotein directly associated with cholesterol metabolism. The ATP binding cassette transporter 1 gene (ABCA1) is one of the major genes modulating plasma levels of HDL-cholesterol (HDL-C). Rare alleles of ABCA1 associated with extreme HDL-C concentrations have not been previously investigated in the Chinese. Methods: Blood samples were collected from 470 subjects whose HDL-C concentrations were within the top 5% of the distribution, 335 subjects in the lowest 5%, and 220 within the range 5%-95%. First, we sequenced all exons of the ABCA1 gene from 50 sub-