Over 800 different missense mutations in the low density lipoprotein (LDL) receptor gene (LDLR) have been identified in patients with familial hypercholesterolaemia (FH). Only two of them, including the Alanine to Threonine change at position 370 (A370T), have been discovered in FH patients but do not cause FH. The frequency of the 370T allele has been reported worldwide to be between 0.022 and 0.070, with no clear association with high cholesterol levels or risk for coronary heart disease (CHD) and stroke. To explore this relationship in more detail we have determined this genotype in 2,659 healthy middle-aged (50-61 years) men participating in the prospective Second Northwick Park Heart Study, with 236 CHD and 67 stroke incident events. The genotype distribution was in Hardy-Weinberg equilibrium and in the no-event group the frequency of 370T was 0.046 (95% CI 0.040-0.052). Overall, there was no significant association of the 370T allele with any measured plasma lipid trait, and there was no difference in genotype distribution or allele frequency between the no-event and CHD (0.059; 95% CI 0.040-0.085) or stroke (0.037; 95% CI 0.012-0.085) groups ( p= 0.18 and 0.65, respectively). There was evidence for significant interaction ( p= 0.006) between body mass index (BMI) and genotype on CHD risk, with 370A homozygotes showing the expected higher CHD risk for those with higher BMI, whilst risk for 370T allele carriers was highest in men in the lowest tertile of BMI. The explanation for this association is unclear, and may simply be chance. Thus, these data confirm the absence of a significant impact of the A370T polymorphism on LDL receptor function, at least as measured by the effect on plasma lipid levels and CHD risk.