The IgA nephropathy Oxford Classification was first published in 2009 by a working group of nephrologists and renal pathologists representing the Renal Pathology Society and International IgA Nephropathy Network. The lesions currently scored include mesangial hypercellularity, endocapillary hypercellularity, segmental sclerosis, tubular atrophy/interstitial fibrosis, and cellular/fibrocellular crescent formation. Two of these lesions, crescent formation (A) and mesangial hypercellularity (B), are shown here.  For the purposes of the Oxford classification, mesangial hypercellularity is defined as >3 mesangial cell nuclei in a mesangial area not adjacent to the vascular pole (in sections cut to 3-micron thickness).