Human immunodeficiency virus (HIV) associated nephropathy (HIVAN) is the most common disease delineated in biopsy series of patients with HIV infection and renal disease. Although the renal histologic lesions in patients with HIV infection present a spectrum of findings, several groups have emphasized characteristic clinical and pathologic features of HIVAN. Consensus has since been reached that HIVAN has a distinctive pathology, consistent with focal segmental glomerulosclerosis, but involving all subunits of the kidney. Several studies have linked the pathogenesis of focal glomerulosclerosis to abnormalities of the glomerular epithelial cell. Recent advances in molecular histologic studies and treatment link the pathogenesis of HIVAN to factors associated with the viral lifecycle. Cytopathic effects of HIV gene products, apoptosis mediated by HIV infection, the elaboration of chemokines and cytokines as a result of viral or host protein synthesis in patients with genetic susceptibility to nephropathy, and the subversion of the host metabolic and synthetic machinery by the virus might be sufficient to create a rapidly progressive disease. If HIV infects and has cytopathic effects on glomerular epithelial cells, and dysfunction of these cells is intimately related to the pathogenesis and progression of renal disease, a reasonable pathogenic mechanism for the development of HIVAN may be inferred. The similarities of HIVAN and the collapsing variant of focal segmental glomerulosclerosis pose the intriguing possibility that the latter is a viral illness as well. The disease is marked by glomerular sclerosis with varying degrees of collapse, tubular epithelial cell degeneration, simplification, microcystic dilatation, interstitial fibrosis and immune cell infiltration. At the level of electron microscopy, tubular reticular inclusions in renal endothelial cells are a typical, but not pathognomonic feature of HIVAN.