Obstructive nephropathy is a relatively common entity that is treatable and often reversible. It occurs at all ages from infancy to elderly subjects. Obstructive uropathy is classified according to the degree, duration and site of the obstruction. It is the result of functional or anatomic lesions located in the urinary tract. The causes of obstructive uropathy are many. Obstruction of the urinary tract may decrease renal blood flow and the glomerular filtration rate. Several abnormalities in tubular function may occur in obstructive nephropathy. These include decreased reabsorption of solutes and water, inability to concentrate the urine and impaired excretion of hydrogen and potassium. Renal interstitial fibrosis is a common finding in patients with long-term obstructive uropathy. Several factors: macrophages, growth factors, hypoxia, cytokines are involved in the pathogenesis of interstitial fibrosis. It has been shown that ACE inhibitors ameliorate the interstitial fibrosis in animals with obstructive uropathy.