The association between pyelonephritis and vesicoureteral reflux (VUR) following pediatric renal transplantation is unclear. To understand the relationship of vesicoureteral reflux with urinary tract infection (UTI) and pyelonephritis, 67 patients were evaluated for reflux and pyelonephritis. Sixty-seven pediatric patients, aged 2 to 18 (39 males and 28 females) underwent renal transplantation. Beginning in 1982, all patients underwent voiding cystourethrography or radionuclide voiding studies 1 to 3 months postoperatively to assess the incidence of VUR. Techniques of ureteroneocystostomy (UNC) included the Leadbetter-Politano (L-p) in 39 cases, and two different modifications of the LICH (herein called LICH-1 and LICH-2) in 30 cases. Urinary cultures were performed routinely. Pyelonephritis was considered present in any patient with UTI and increased serum creatinine or fever greater than 38.5. VUR occurred in 36% of patients; highest in LICH-1 (79%), intermediate in L-P (22%), and lowest in LICH-2 (9%). VUR was not statistically significantly higher in females (43%) v males (31%). UTI occurred in 37% of patients. The difference in incidence between females (54%) and males (26%) was significant (P less than .05). The frequency of UTI in patients with VUR was 46% v 33% in patients without reflux (NS). However, pyelonephritis that occurred in 16% of cases overall was present in 82% of UTIs in patients with reflux v 14% of UTIs in patient without reflux (P less than .01). Pyelonephritis is significantly increased in pediatric renal transplant patients with UTI was have VUR. A nonrefluxing UNC is advocated in all patients. All renal transplant patients should have routine monitoring of urinary cultures and should be evaluated of VUR posttransplant.