This randomized controlled clinical trial evaluated whether furosemide-assisted forced diuresis during flexible ureteroscopy reduced the residual fragment rate and improved stone clearance in patients with renal stones measuring up to 30 millimeters. Adult patients undergoing flexible ureteroscopy were randomized into two parallel groups: an experimental group that received intravenous furosemide during the procedure and a control group that received standard perioperative and postoperative care without furosemide. Residual stone fragments were assessed using low-dose non-contrast computed tomography on postoperative day 1 and at 6 weeks after the procedure. The primary outcome was the proportion of patients with residual stone fragments greater than 2 millimeters on postoperative day 1. Secondary outcomes included the proportion of patients with residual stone fragments greater than 2 millimeters at 6 weeks, operative time, length of hospital stay, postoperative complications, total urine output during the first 24 hours, and the need for auxiliary treatment for clinically significant residual stones.