An international group of authors summarizes evidence from epidemiological and clinical trial studies that apolipoprotein B is superior to standard cholesterol indices for identifying those at increased risk of vascular disease and judging the effectiveness of lipid-lowering therapy. This is likely because apolipoprotein B provides a measure of the number of atherogenic particles. Evidence is also reviewed that in patients without symptomatic vascular disease or diabetes, the apolipoprotein B/apolipoprotein AI ratio is superior to conventional cholesterol ratios for evaluating lipoprotein-related risk of vascular disease.