OBJECTIVE Miniaturization of percutaneous nephrolithotomy techniques have led to their increased consideration for lower pole renal stones that can prove more challenging to reach using retrograde intrarenal surgery. The objectives of the present study were to evaluate and compare the outcomes of miniaturized percutaneous nephrolithotomy (miniPCNL) and retrograde intrarenal surgery (RIRS) for the treatment of lower pole renal stones. METHODS A retrospective study was performed in two academic urology departments between January 2016 and June 2019. Patients presenting with one or multiple stones of the lower calyx and/or renal pelvis, between 10 and 40mm based on CT-scan treated by miniPCNL or RIRS were included. RESULTS In all, 115 miniPCNL and 118 RIRS procedures were included. The rate of patients with no significant residual fragment (stone free rate) after the first procedure was higher in the miniPCNL group (69% vs. 52% P=0.01), especially for stones>20mm (63% vs. 24% respectively, P<0.001) and stones with a density≥1000HU (69% vs. 42% respectively, P=0.009). The higher stone free rate of miniPCNL was confirmed in multivariate analysis, adjusting for stone size and number of stones, OR 4.02 (95% CI 2.08-8.11, P<0.0001). The overall postoperative complication rate was higher in the miniPCNL group than in the RIRS group (23% vs. 11%, P=0.01). A second intervention for the treatment of residual fragments was necessary for 9.6% of patients in the miniPCNL group versus 30.5% of patients in the RIRS group (P<0.001). Pre-stenting rate and duration of ureteral drainage (2 [1-8] vs. 25 days [7-37], P<0.001) were lower in the miniPCNL group. CONCLUSIONS The stone free rate was higher after miniPCNL, especially for stones>20mm and with a density>1000 HU, but was associated with a higher risk of postoperative complications and a longer hospital stay. RIRS resulted in fewer complications at the cost of a higher retreatment rate and longer ureteral stenting. METHODS 3.