Lipoprotein(a) is a highly atherogenic particle. The plasma concentrations of this lipoprotein are strongly related to a genetically determined size polymorphism of apolipoprotein(a). This article reviews some pathogenetic characteristics of the apolipoprotein(a) polymorphism besides its known effect on the lipoprotein(a) plasma concentrations. Those are the relation of the apolipoprotein(a) phenotype with atherogenesis, the apolipoprotein(a) phenotype-specific elevation of lipoprotein(a) in hemodialysis patients and the advantages of this polymorphism for the atherosclerosis risk evaluation in high-risk patients. It furthermore discusses the observed association between the low molecular weight apolipoprotein(a) phenotype and Type I diabetes mellitus.