The R219K polymorphism in the ATP-binding cassette transporter 1 gene ( ABCA1) has been associated with reduced severity of atherosclerosis, fewer coronary events, decreased triglycerides and a trend to increased HDL in men with coronary heart disease (CHD). This study examined the frequency and the effect on CHD and plasma lipids of the polymorphism in patients of both sexes attending a lipid out-patient clinic. The overall frequency of the K allele was 0.26. It was lower in patients with CHD (0.21) than in those without (0.27) but this was not statistically significant. Amongst patients with elevated Lp(a) the frequency of the K allele was significantly lower in those with CHD (0.16) than in those without (0.29). There were no statistically significant differences in total cholesterol, LDL, HDL, apoB or apoAI between carriers and non-carriers. When patients with probable secondary hypertriglyceridaemia (triglycerides >1000 mg/dl), type 2 diabetes and carriers of lipoprotein lipase polymorphisms associated with hypertriglyceridaemia were excluded, the K allele was significantly associated with reduced triglycerides but only in patients with apoE 3/3 genotype. In conclusion, we provide additional evidence that the R219K polymorphism in the ABCA1 gene either directly or as a result of linkage disequilibrium with additional functional variant(s), has a protective effect against CHD and is associated with lower plasma triglycerides in sub-groups of patients with hyperlipidaemia.