We evaluated the clinical value of flexible ureteroscopic lithotripsy for the treatment of upper urinary tract calculi in infants. Fifty-five infants with upper urinary tract calculi were included in this study: 41 males and 14 females. Retrograde intrarenal surgery was performed by an 8 Fr/30cm flexible ureterorenoscope (POLY (R)) combined with a holmium laser. CT scanning or radiography of the kidneys, ureters, and bladder region was performed one month after the operation to confirm the clearance of calculi. All the 55 infants with calculi in 74 sides underwent 66 flexible ureteroscopic lithotripsy procedures. The median operation time was 30 min. The median amount of flushing fluid was 500 mL. The stone-free rate after a single session treatment was 94.6%, within which 10 infants underwent simultaneous bilateral flexible ureteroscopy lithotripsy. Catheters were retained in 45 infants for 24-48 h after the operation. Continuous high fever due to reflux was present in two cases. Flushing fluid extravasation was found in one infant. Some patients with minor complications, such as mild hematuria, irritation symptoms, and low fever, recovered without treatment. The duration of hospitalization time after the operation was approximately 1-5 days. Flexible ureteroscopic lithotripsy is a safe, highly efficient, minimally invasive, and reproducible operation for removal of upper urinary tract calculi in infants. This technique is a convenient method for postoperative management of patients that enhances their rapid recovery. It is a promising option for therapy of infants ineffectively treated by extracorporeal shockwave lithotripsy.