Statins decrease cardiovascular morbidity and mortality, essentially, by reducing LDL-cholesterol levels and, additionally, by increasing HDL-cholesterol concentrations. Environmental and genetic factors are known to affect LDL-C response to statins but less is known regarding HDL-C. We have evaluated the lipid and lipoprotein response to 20 mg/day of pravastatin for 16 weeks in relation to the G/A polymorphism in the promoter region of the apo A-I gene in 397 hypercholesterolaemic subjects followed-up on an out-patient basis. In the study population, 61.7% were homozygous for the G allele and 36% were heterozygous. The A allele carriers had an HDL-C 6.5% higher than the G allele homozygotes (P=0.021 in univariate analysis; P=0.009 in multivariate analysis). However, on segregation by gender and smoking status the effect was significant only in non-smoking males. The A allele carriers did not increase their HDL-C concentrations after treatment (-0.3, 95%CI -3.3 to 2.7%) while G allele homozygotes had a 4.9% increase (95%CI 2.5-7.3%). Differences in the response between both groups were significant before (P=0.008) and after adjustment for confounding variables such as age and baseline HDL-C concentration (P=0.046). We conclude that the G/A polymorphism of the apo A-I promoter region affects not only baseline HDL-C concentrations but also its response to pravastatin treatment.