Background: Postoperative pain following retrograde intrarenal surgery (RIRS) for kidney stones is a multifactorial clinical challenge. Identifying patient-, stone-, and operation-related predictors is essential for preoperative risk stratification and optimal pain management. This single-center prospective study investigated the correlation between various factors and postoperative pain severity in patients undergoing RIRS at Fortis Hospital, Mohali. Methods: Ninety-seven patients aged 18–65 years with radiologically confirmed renal stones undergoing RIRS were prospectively enrolled between March 2021 and September 2022. Preoperative demographic and clinical data (including NCCT KUB findings, stone characteristics, preoperative DJ stenting status, and hydronephrosis) were recorded. All patients underwent RIRS with a 7.5 Fr flexible digital ureteroscope and Holmium:YAG laser lithotripsy; a ureteral access sheath was used routinely. Postoperative pain was measured using the visual analogue scale (VAS) at the 6th, 12th, and 24th hour. Patients were divided into two groups: Group I (VAS <7) and Group II (VAS ≥7), with additional analgesia provided as needed. Data were statistically analyzed using IBM SPSS version 25, with a significance level of p < 0.05. Results: Out of 97 subjects, 82 patients (84.5%) had VAS scores <7, and 15 patients (15.5%) reported VAS scores ≥7. Demographic parameters, stone number, location, size, and preoperative hydronephrosis did not show significant differences between the groups (p > 0.05). However, a statistically significant association was identified between the size of the ureteral access sheath and the indwelling time with higher postoperative VAS scores (p = 0.027 and p = 0.043, respectively). The study findings underscore that prolonged sheath indwelling time and use of smaller-diameter sheaths are potential independent predictors of postoperative pain. Conclusion: Our data suggest that while many preoperative factors are comparable between patients with low and high postoperative pain, operation-related technical variables significantly influence pain outcomes post-RIRS. Preoperative identification of patients at high risk for severe pain may guide individualized intraoperative strategies and postoperative analgesia protocols.