We report the case of a 3-year-old boy with urinary tract malformation (left sided stenosis of the ureteropelvic junction) which was precipitating factor for ensuing nephrolithiasis of the left kidney during the therapy with ceftriaxone. The treatment with spasmolytics was initiated, together with the forced parentheral hydration. After 3 weeks, there was no evidence of calculi in the urinary tract.