<prompt> Most common cause of renal scarring in a 3 year old child is-Pelviureteric junction obstructionVesicoureteric refluxUrinary tract infectionPosterior urethral valves  <response>: Ans. is b i.e., Vesicoureteric reflux Most common cause of renal scarring in a 3 year old child: VUR induced pyelonephritis. Renal scarring is most commonly a result of chronic pyogenic infection of the kidney or chronic pyelonephritis. Chronic pyelonephritis occurs only in patients with major anatomic abnormalities, such as obstructive uropathy, struvite calculi or, most commonly, VUR in 30 to 45 of young children with symptomatic UTI. 