Given the high prevalence of the atherogenic forms of apolipoprotein B (apoB) dyslipoproteinemias and the effectiveness of appropriate therapy, we feel that access for all physicians to simple, effective diagnostic aids that enable use of widely available technology is vitally important in clinical lipidology. In this Review, therefore, we present a diagnostic algorithm for the diagnosis of these disorders that is based on concentrations of total cholesterol, triglyceride and apoB. By including apoB values, lipoprotein number and composition can be deduced and each of the classic dyslipoproteinemias identified. All three parameters can be accurately and inexpensively determined in clinical laboratories and, therefore, this algorithm can be used by any physician to make an accurate diagnosis without use of specialist research laboratories. Just as the application of LDL cholesterol measurement moved clinical practice forward from plasma lipids to lipoprotein lipids, we believe that the use of apoB will further advance diagnosis and treatment of dyslipoproteinemias.