OBJECTIVE To describe the technique and outcomes of supine percutaneous nephrolithotomy (PCNL) in the Galdako-modified Valdivia position. MATERIALS AND METHODS Prospective data were collected from 303 patients undergoing PCNL in the Galdako-modified Valdivia position at our institution between 2007 and 2015. We report our technique with outcomes of operative times, stone-free rate (SFR), and complications. RESULTS A total of 202 solitary stones with a mean size of 17.19 ± 5.82 mm, 42 stones in multiple calices, and 57 staghorns were treated. Mean operative time was 79.79 ± 35.72 minutes. A total of 244/303 (80.5%) patients had clearance or <2 mm stone on postoperative CT. Minor complications (Clavien-Dindo Classification [CDC] 1-2) occurred in 59 (19.5%) cases and major complications (CDC ≥3) occurred in 22 (7.3%) cases. Five (1.7%) cases required postoperative blood transfusion for bleeding complications. CONCLUSION We demonstrate that PCNL in a high-volume center to be safe and efficacious in the Galdalko-modified Valdivia position. We show equivalent SFR and complication rates to large studies of prone PCNL, with potential to decrease operative time. In particular, supine position is optimum for obese or high-risk patients with complex stone disease, because of ease of positioning and lower theoretical risk of anesthetic complications.