The safe duration of warm ischemia during partial nephrectomy remains controversial. Our aim was to evaluate the short- and long-term renal effects of warm ischemia in patients with a solitary kidney. Using the Cleveland Clinic and Mayo Clinic databases, we identified 362 patients with a solitary kidney who underwent open (n=319) or laparoscopic (n=43) partial nephrectomy using warm ischemia with hilar clamping. Associations of warm ischemia time with renal function were evaluated using logistic or Cox regression models first as a continuous variable and then in 5-min increments. Median tumor size was 3.4 cm (range: 0.7-18.0 cm), and median ischemia time was 21 min (range: 4-55 min). Postoperative acute renal failure (ARF) occurred in 70 patients (19%) including 58 (16%) who had a glomerular filtration rate (GFR) <15 ml/min per 1.73 m(2) within 30 d of surgery. Among the 226 patients with a preoperative GFR >or=30 ml/min per 1.73 m(2) and followed >or=30 d, 38 (17%) developed new-onset stage IV chronic kidney disease during follow-up. As a continuous variable, longer warm ischemia time was associated with ARF (odds ratio: 1.05 for each 1-min increase; p<0.001) and a GFR<15 (odds ratio: 1.06; p<0.001) in the postoperative period, and it was associated with new-onset stage IV chronic kidney disease (hazard ratio: 1.06; p<0.001) during follow-up. Similar results were obtained adjusting for preoperative GFR, tumor size, and type of partial nephrectomy in a multivariable analysis. Evaluating warm ischemia in 5-min increments, a cut point of 25 min provided the best distinction between patients with and without all three of the previously mentioned end points. Limitations include the retrospective nature of the study. Longer warm ischemia time is associated with short- and long-term renal consequences. These results suggest that every minute counts when the renal hilum is clamped. (c) 2010 European Association of Urology. Published by Elsevier B.V. All rights reserved.