Urinary tract obstruction in the developing human fetus is an important cause of postnatal kidney failure and is the most common cause of end-stage renal disease and chronic renal failure in boys less than 4 years of age. Although the pathogenesis of renal dysplasia resulting from urinary tract obstruction is not well defined, it is clear that the earlier the obstruction occurs during in utero nephrogenesis the more severe the histopathological changes. Efforts to intervene in the human fetus have been hampered by an inaccuracy of diagnosis and by a lack of validation of in utero features predictive of poor outcome. A number of experimental models of obstructive renal dysplasia have been developed, which result in the consistent histopathological features of tubular cell apoptosis, mesenchymal expansion with mesenchymal myocyte transformation, and decreased glomerular endowment and glomerular injury. Defining the optimal timing of release of obstruction and restoring normal developmental gene and protein patterns should guide future intervention in these processes. Experimental animal models that closely simulate human development and disease will, thus, be essential for exploring these questions, and for assessing novel fetal therapies for future human application.