The renal biopsy technique has made it possible to classify lupus nephritis into its varied forms. Utilizing light histology, immunofluorescence microscopy, and ultrastructural techniques, the following renal morphological manifestations of systemic lupus erythematosus can be identified: mesangial abnormalities; focal proliferative, diffuse proliferative and membranous glomerulonephritis; glomerular sclerosis; interstitial nephritis; vascular sclerosis and necrotizing renal vasculitis. Each of the morphological forms is associated with distinctive clinical features and prognosis. Mesangial and focal proliferative lupus nephritis may occur in the absence of clinical abnormalities, and in general have a favorable prognosis. Diffuse proliferative lupus nephritis often is manifested by the nephrotic syndrome and renal functional impairment which proves to be irreversible and progressive. Transition from the milder forms to diffuse proliferation occurs in about one-sixth of patients. Membranous lupus nephritis is characterized by the nephrotic syndrome, which often is persistent, but renal functional impairment develops slowly and is rarely severe. Necrotizing vasculitis, which supervenes on occasion during the course of diffuse proliferative lupus nephritis, produces the clinical picture of malignant hypertension and progresses rapidly to uremia. Interstitial nephritis usually occurs in combination with one of the glomerular forms, but at times may be the predominant renal lesion both morphologically and clinically. Glomerular sclerosis, often associated with hypertension and vascular sclerosis, commonly develops in the course of lupus nephritis, especially in the more severe forms, and may progress even though active disease has remitted. An awareness of clinico-pathologic correlations in lupus nephritis provides a basis for intelligent management and critical assessment of therapy.