In the August 2001 issue of the Journal (J Med Genet 2001;38:536-40), in the Letter by Horvath et al on “High frequency of the ApoB-100 R3500Q mutation in Bulgarian hypercholesterolaemic subjects”, the estimated prevalences of the R3500Q mutation in the Czech Republic and Slovakia, shown in fig 2, have been transposed and the correct prevalences should be “no data available” for Slovakia and 1:250-1:350 for the Czech Republic. The authors apologise for this error.