ObjectiveTo investigate the clinical efficacy and safety of lithotripsy under flexible ureteroscope using 200 μm holmium laser for medullary sponge kidney stones. MethodsWe identified and retrospectively reviewed 10 patients who underwent flexible ureteroscopic lithotripsy for medullary sponge kidney calculi between January 2013 and July 2014. The remission of clinical symptoms and incidence of perioperative complications were observed. ResultsThe staged surgery was performed on 10 bilateral cases with one session for each kidney. The operative time of our cohort was 130-180 minutes. The postoperative average hemoglobin was not significantly reduced (110.6 g/L) as compared with preoperative average hemoglobin (116.8 g/L) (P>0.05). Two patients had fever after operation and temperatures became normal by anti-infection. The renal function and plain film of kidney-ureter-bladokr (KUB) and CT scan were rechecked for all cases on three months after operation. The kidney function in 3 cases of chronic renal failure was ameliorated to varying degrees. The postoperative average of serum creatinine (196.2 μmol/L) was reduced as compared with the preoperative average serum creatinine (385.7 μmol/L) (P<0.05). Six patients reported spontaneous discharge of residuary stones during three months after surgery. KUB and CT scan proved significant reduction of the loads of stones for all cases after operation. ConclusionFlexible ureteroscope with 200 μm holmium laser lithotripsy is a safe and effective treatment for medullary sponge kidney stones based on its effect on amelioration of symptom and renal function.