Supernumerary kidney is the rarest of all renal anomalies; fewer than 80 cases have been reported in the literature over the years. Supernumerary kidneys are most commonly located on the left side of the abdomen. Different pathologic conditions are reported to affect supernumerary kidneys and they may be associated with malformations of the upper urinary tract and genital tract. Because of their infrequent occurrence and reporting, they frequently cause diagnostic challenges. Here we report a case in a 14-year-old male patient of unilateral supernumerary kidney on the right side of the abdomen with multiple calculi, mal-rotation and a gross hydronephrotic left kidney.