Juvenile onset renal disease is described in 2 male and 2 female young Rottweiler dogs. Histologic changes in all dogs were cystic dilatation of Bowman's space, mesangial hypercellularity, and glomerulosclerosis. Three dogs also had glomerular crescents and moderate to severe interstitial fibrosis. Electron microscopy revealed glomerular basement membranes of variable thickness, with extensive splitting or lamellation of the lamina densa. These ultrastructural findings are similar to those found in people and in other breeds of dogs with inherited defects in type IV collagen.