Whether national guidelines should incorporate apolipoprotein B (apoB) into clinical practice is one of the most important and contentious decisions they must face. Canada has chosen to do so. What Europe and America decide remains to be seen.Obviously, the results of the major epidemiological studies and clinical trials should be major drivers of decisions about guidelines. Such evidence clearly indicates that apoB is superior to LDL C as a marker of risk and an index of the adequacy of therapy but is mixed as to whether apoB is superior to non-HDL C. In this paper, we demonstrate that the issue is more complicated than it appears: that even if non-HDL C and apoB are equal predictors of vascular risk (which we do not believe is the case), this is not due to the VLDL C that is included in non-HDL C but rather reflects the fact that non-HDL C is a 'backwards' measure of apoB - that is, non-HDL C provides an indirect estimate of LDL particle number. Moreover, equal predictive power in groups does not mean that markers have equal predictive power in individuals. We also list multiple clinical circumstances when non-HDL C and apoB lead to different clinical decisions because the real test of markers is when they differ, not when they agree.Thus, our conclusion is that apoB and non-HDL C are equal - except when they are not. Because apoB allows greater specificity of diagnosis and therapy, it re-establishes the primacy of individuals over groups as the objects of our study and our care and that may be its most important contribution to clinical lipidology.