The immunopathology, clinical characteristics, natural history, and treatment of the lesions that constitute the heterogeneous group of primary proliferative glonerulonephritis have been reviewed. These lesions include pure mesangial proliferative glomerulonephritis, IgA nephropathy, mesangiocapillary glomerulonephritis, focal and segmental proliferative glomerulonephritis, and crescentic glomerulonephritis. A great deal is now known concerning the natural history of these individual entities and some have responded satisfactorily to a variety of therapeutic modalities. Unfortunately, the most common of the proliferative glomerulonephritides, namely, IgA nephropathy, has not yet yielded to therapeutic efforts, except on rare occasions. It is hoped that, through better understanding of the fundamental pathogenetic mechanisms involved and a continued search for etiologic events, better and more effective therapeutic regimens will be devised. Considering the rate of progress that has occurred in the last several decades, there is good reason for optimism that ultimately these proliferative glomerulonephritides that contribute so importantly to the pool of patients with end-stage renal disease will ultimately be controlled or even prevented.