Crim1 hypomorphic (Crim1 ^ KST264/KST264 ) mice display progressive renal disease characterized by glomerular defects, leaky peritubular vasculature, and progressive interstitial fibrosis. Here we show that 27 of these mice also present with hydronephrosis, suggesting obstructive nephropathy. Dynamic magnetic resonance imaging using Magnevist showed fast development of hypo-intense signal in the kidneys of Crim1 ^ KST264/KST264 mice, suggesting pooling of filtrate within the renal parenchyma. Rhodamine dextran (10 kDa) clearance was also delayed in Crim1 ^ KST264/KST264 mice. Pyeloureteric peristalsis, while present, was less co-ordinated in Crim1 ^ KST264/KST264 mice. However, isolated renal pelvis preparations suggest normal pelvic smooth muscle contractile responses. An analysis of maturation during the immediate postnatal period [postnatal day (P) 0-15] revealed defects in papillary extension in Crim1 ^ KST264/KST264 mice. While Crim1 expression is weak in pelvic smooth muscle, strong expression is seen in the interstitium and loops of Henle of the extending papilla, commencing at the tip of the P1 papilla and disseminating throughout the papilla by P15. These results, as well as implicating Crim1 in papillary extension and pelvic smooth muscle contractility, highlight the previously unrecognized association between defects in papillary development and progression to chronic kidney disease later in life. Copyright (c) 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley Sons, Ltd.