Background: Partial nephrectomy (PN) is now the gold standardfor the surgical treatment of small renal masses. We evaluated theeffect of WIT and other factors on RDF assessed by preoperativeand postoperative renal scintigraphy.Methods: Between 2003 and 2008, 182 consecutive laparoscopicPN (LPN) were performed in an academic centre. Among those,56 had mercaptoacetyl triglycine (MAG3) lasix renal scintigraphypreoperatively and postoperatively.Results: Medians for age, preoperative estimated glomerular filtrationrate and computed tomography scan tumour size were 62years, 82 mL/min/1.73m2 and 26 mm, respectively. Median WITand preoperative RDF were 30 minutes and 50%, respectively.Median loss of RDF after surgery was 14%. Linear regression curvesshowed that loss in RDF rate was 0.2% per minute when WIT was<30 minutes and 0.7% per minute when WIT was ≥30 minutes.In multivariate analysis, length of WIT and endophytic tumourlocation were associated with a statistically significant loss of RDF(p < 0.05), but only in the group who experienced >30 minutesof WIT.Interpretation: Our results suggest that the factors associated withloss of RDF are not the same before and after 30 minutes of WITand that the rate of loss in RDF increases after 30 minutes. Since,the effect of WIT is small up to 30 minutes, we believe that surgeryshould focus on limiting the resection of normal parenchymaand to ensure negative margins and hemostasis, rather than onpremature unclamping.