310 Background: The quality of transurethral resection of bladder tumors strongly determines patient’s tumor after-care and prognosis. En bloc resection of bladder tumors (ERBT) might improve staging quality, perioperative morbidity and influence tumor recurrence. This is the first European multi-center study which was initiated by ESUT and was conducted to evaluate the safety, efficacy and recurrence rates of electrical vs. laser ERBT. Methods: Transurethral ERBT was performed on 221 prospectively collected patients in six academic centers with either monopolar/bipolar current or holmium/thulium laser energy. Staging quality measured by detrusor muscle involvement, various perioperative/surgical parameters and 12 months follow-up data were analyzed. Results: 156 and 65 patients were treated with electrical and laser ERBT, respectively. Median tumor size was 2.1 cm with biggest up to 5 cm. Detrusor muscle was available in 97.3%. A switch to conventional TURBT was significantly more frequent in the electrical ERBT group (26.3% vs. 1.5%, p<0.001). Median operation duration (25 min), postoperative irrigation (1 day) and catheterization time (2 days) as well as hospitalization (3 days) were similar in both groups. Overall complication rate was low (Clavien ≥3, n=6 (2.7%)). Hemoglobin was significantly more decreased after electrical ERBT (p=0.0013), however overall hemoglobin loss was not clinically relevant (0.38 g/dl). 148 patients with first diagnosis of urothelium carcinoma of the bladder were followed for 12 months of which 33 (22.3%) recurred. 63.6% of recurrences occurred out of the ERBT resection field. No difference was noticed between both ERBT groups. Conclusions: ERBT is safe and reliable regardless of the energy source used and offers high quality resections of tumors >1 cm. Recurrence rates did not differ within both groups although the majority of recurrences were noticed out of the ERBT resection field. Laser device might be an alternative for the treatment of patients with higher risk of postoperative bleeding due to its efficient hemostatic effect.