Introduction: Controversy exists regarding follow-up investigations in children diagnosed with their first pyelonephritis. In our centre children with upper urinary tract infections are subjected to a DMSA or MAG3 scan to assess renal parenchymal damage app. 6 months following the UTI. We aimed to analyse follow-up data on 179 consecutive Danish children after their first pyelonephritis. Material and methods:We examined the records of children diagnosed with their first upper UTI confirmed by urine culture during the years 2011-2013.We collected data on the clinical course of the pyelonephritis, the results of the DMSA and MAG3 scans as well as renal ultrasound scans. All children with known congenital renal and urinary tract malformations where excluded from the analysis. Results: Of the initial population (age 2 months to 14 years), only 9 (5%) children presented with abnormal US scan (3 with bilateral and 6 with unilateral hydronephrosis). Twenty-one children (12%) presented with parenchymal defects in the DMSA/MAG3 scans (17 unilateral, 4 bilateral). Fifteen children (8%) all with scars presented with an uneven renal differential function on renal scans (<40/60). Of these patients, 9 underwent a VCUG and in all reflux was confirmed, 8 unilateral (n=3 grade V, n=3 grade IV, n=1 grade III, n=1 grade II) and 1 bilateral reflux (grade IV). Six of these patients underwent endoscopic reflux treatment.Of the 21 children with DMSA/MAG3 abnormalities only 5 presented with abnormalities in renal ultrasound (2 with bilateral hydronephrosis, 3 with unilateral hydronephrosis). Conclusions: Renal DMSA/MAG3 scans are important tools when assessing differential renal function and renal parenchymal defects following a pyelonephritis.Whether to perform these investigations already after the first pyelonephritis is still under debate. We find a considerable number of children (12%) with clinically significant abnormalities in DMSA/MAG3 scans following their first pyelonephritis.