OBJECTIVE To develop an animal model of chronic progressive hydronephrosis; to establish patterns of diuretic renography during development of the condition; and to relate renographic abnormality to morphological change in the renal parenchyma. METHODS The cellophane sclerosis technique was used to produce a hydronephrosis in the left kidney of six rabbits. Post-operatively MAG3 diuretic renography was performed at weekly intervals. When a steady renographic trend was noted the rabbits were killed and the kidneys examined histologically. RESULTS Four rabbits had persistent type II renographic curves on the left for 12 weeks. The measured split renal function fell steadily to < 20% in this time. Morphologically there was hydronephrosis with marked structural changes in the parenchyma seen on histological examination. Two rabbits had stable type IIIa renographic drainage patterns on the left with preserved renal function. Morphologically there was hydronephrosis but histologically the kidneys were normal. There were no renographic or structural changes in a control rabbit after a sham laparotomy. CONCLUSIONS The cellophane sclerosis technique can be used to create a reproducible chronic progressive hydronephrosis. In this animal model hydronephrosis and a persistent type II curve are associated with renographic evidence of deteriorating renal function and disruption of renal architecture histologically. Hydronephrosis and a type IIIa curve are associated with preservation of normal renal function and histological structure.