Background: Urinary tract infections (UTIs) are very common in children. Several biomarkers have been used for the diagnosis of UTI and prediction of renal parenchymal involvement. Objectives: This study aimed to evaluate plasma D-dimer as a diagnostic marker of UTI in children. Methods: This cross-sectional study included 41 children aged 1 month to 14 years with their first febrile UTI confirmed by positive urine culture referred to Bandar Abbas Children’s Hospital, Iran, from October 1, 2017, to April 1, 2018. Participants’ demographic features, including age and gender were recorded. White blood cell (WBC) count, percentage of neutrophils, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum D-dimer were measured in random blood samples for all the patients. Results: Out of 41 children (mean age: 5.50 ± 4.01 years) evaluated in this study, 6 (14.6%) were male, and 35 (85.4%) were female. The mean plasma D-dimer level was 1496.49 ± 2787.55 µg/L. A significant positive correlation was found between D-dimer with ESR (r = 0.647, P = 0.026) and CRP (r = 0.525, P = 0.001). Plasma D-dimer was not associated with age; however, age was inversely correlated with WBC count (r = -0.327, P = 0.037). No significant relationship was found between plasma D-dimer, ESR, CRP, WBC count, and neutrophil percentage with gender (P > 0.05). Conclusions: According to our results, in children aged 1 month to 14 years with culture-confirmed UTI, plasma D-dimer is positively correlated with ESR and CRP. Nevertheless, D-dimer appears not to be influenced by age or gender. Further studies are required to confirm the utility of D-dimer as a diagnostic marker of UTI in children.