Berrettini A, et al. - The topic of exploration herein, was the safety and efficacy of retrograde intrarenal surgery (RIRS) using ureteral access sheath (UAS) in children weighing < 20 kg. This approach appeared to be an effective and safe procedure for treating kidney stones in pre-school patients weighing < 20 kg without complications at both short and long-term follow up. Stones of mixed composition located in the lower polar calices illustrated a link with a greater risk of postoperative complications.