Study objectiveWe evaluated the effect of vitamin C administration on postoperative catheter-related bladder discomfort (CRBD). DesignA double-blind, randomized controlled trial. SettingUniversity tertiary hospital. PatientsThe participants were patients undergoing transurethral resection of bladder tumor. InterventionPatients were randomly assigned to either vitamin C (n = 59) or control (n = 59). The vitamin C group received 1 g of vitamin C intravenously and the control group received normal saline, administered after the induction of anesthesia. MeasurementsThe primary endpoint was moderate or greater CRBD immediately postoperatively. Secondary outcomes included the incidence of moderate or greater CRBD at 1, 2, and 6 h postoperatively. The symptom of CRBD is either a burning sensation with an urge to void or discomfort in the suprapubic area. Moderate CRBD was defined as spontaneously reported by the patient without any behavioral responses, such as attempts to remove the urinary catheter, intense verbal reactions, and flailing limbs. Severe CRBD was spontaneously reported by the patient with behavioral responses. Patient satisfaction scores were also evaluated. Main resultsThe group that received vitamin C exhibited a significantly lower incidence of moderate or greater CRBD immediately postoperatively compared with the control group (17 [28.8%] vs. 40 [67.8%], p < 0.001, relative risk [95% confidence interval] = 0.426 [0.274–0.656]). The vitamin C group also showed a significantly lower incidence of moderate or greater CRBD at 1 and 2 h postoperatively compared with the control group (10 [16.9%] vs. 25 [42.4%], p = 0.003; and 5 [8.5%] vs. 16 [27.1%], p = 0.008, respectively). However, there was no significant difference in the incidence of moderate or greater CRBD 6 h postoperatively. Patient satisfaction scores were significantly higher in the vitamin C group than in the control group (5.0 ± 1.3 vs. 4.4 ± 1.4, p = 0.009). ConclusionsPatients who received vitamin C had decreased CRBD and improved patient satisfaction following transurethral resection of bladder tumor.