Background.Fluid overload is a major complication during surgical hysteroscopy and transurethral resection of the prostate. We evaluated the role of temperature on absorption of the irrigation solution (IRRSOL) in endoscopic surgery when warm fluids are used to minimize hypothermia. Methods.We measured the density and dynamic fluidity of five IRRSOLs (0.9% saline, Ringer’s lactate, 1.5% glycine, 5% dextrose, and 2.5/0.54% sorbitol/mannitol) at three different temperatures (178C, 278C, and 378C). Next, a hypothetical typical endoscopic resection surgery was defined as the reference: total IRRSOL absorption (750 ml), resection time (30 min), and IRRSOL temperature (178C). On the basis of Poiseuille’s law, we calculated new values for intravasation using the predetermined dynamic fluidity values at 278C and 378C to assess the influence of the IRRSOL temperature on intravascular absorption (under identical conditions) and then estimated the time to reach fluid overload at each temperature with both electrolyte and non-electrolyte IRRSOLs. Results.Density and fluidity varied with temperature. In these specific conditions, when the temperature of the IRRSOL was increased from 178Cto 378C, the mean absorption rate was predicted to increase about 54% and the theoretical ‘safe’ duration of surgery decreased by 65%, for both electrolyte and non-electrolyte IRRSOLs. The reduction in the ‘safe’ duration of surgery averaged 21.1 min for non-electrolyte IRRSOL (reduced from 60.0 to 38.9 min) and 35.2 min when electrolyte IRRSOLs were used (reduced from 100.0 to 64.8 min). Conclusions.Compared with cold fluids, isothermic IRRSOL may increase the risk of fluid overload because dynamic viscosity decreases at higher temperatures.