Objective: This study aimed to investigate the effect of stone density on the success of ureterorenoscopy (URS) and retrograde intrarenal surgery (RIRS). Materials and Methods: The data of patients who underwent URS or RIRS due to kidney and ureteral stones between January 2013 and March 2018 were retrospectively screened. For all patients, age, gender, comorbidities, the American Society of Anesthesiologists (ASA) score, the presence of preoperative double-J (DJ) stents, extracorporeal shock wave lithotripsy (ESWL) history, ipsilateral stone surgery history, the presence of renal anomalies, stone laterality, stone opacity, stone density, stone size, stone volume, operative time, stone-free status, and the presence and size of residual stones were recorded. Results: The study included 566 patients who underwent URS or RIRS, including 186 women (32.9%) and 380 (67.1%) men. The mean age of the patients was 47 years. The mean stone size was 10 mm, and the mean stone density was 886 Hounsfield units. The mean stone volume was 426.13 mm3. The mean operative time was 31 minutes. The stone-free rate was 89.4%. Stone density, stone size, and stone volume were positively correlated with operative time (p<0.001) and residual stone size (p<0.001). Additionally, stone density and residual stone size were positively correlated in the group that did not achieve stone-free status (p=0.003). Conclusion: In this study, it was determined that stone density, stone size, and stone volume were positively correlated with residual stone size and operative time. In addition, stone density was positively correlated with residual stone size among patients who were not stonefree after treatment, indicating that high stone density negatively affects the success of treatment even in cases presenting with small stone size and volume preoperatively.