Purpose <p>Vitamin D plays an important role in immune regulation and may help prevent urinary tract infection (UTI). This study aimed to explore the impact of vitamin D supplementation on preventing recurrent UTI in children.</p> Methods <p>This prospective case-control study included 18 school-aged children with recurrent UTI and 19 healthy children. Serum vitamin D levels were compared between the groups. Vitamin D supplementation was administered to children with recurrent UTI. Vitamin D concentrations before and after supplementation, and recurrence frequency during the study period, were evaluated.</p> Results <p>The mean serum vitamin D levels in the patient group were lower than those in the healthy control group (15.89 ± 6.76 vs. 19.96 ± 10.08 ng/mL), but this difference was not statistically significant (<i>p</i> = 0.16). However, vitamin D deficiency was significantly more prevalent in the patient group (88.9% vs. 36.8%, <i>p</i> = 0.002). Serum vitamin D levels increased significantly after supplementation (15.89 ± 6.76 vs. 19.96 ± 8.77 ng/mL, <i>p</i> = 0.04) and the proportion of patients with vitamin D deficiency decreased significantly (%88.9 vs. %38.9, <i>p</i> = 0.004). The median number of UTI episodes declined significantly (2.0 vs. 1.5 episodes, <i>p</i> = 0.014).</p> Conclusion <p>Vitamin D deficiency appears to be more common in children with recurrent UTI. Vitamin D supplementation significantly increased serum vitamin D levels and was associated with a reduction in recurrent UTI frequency based on a pre–post comparison within the patient group. Correcting vitamin D deficiency and maintaining adequate levels may be a simple and effective method for preventing recurrent UTI in school-aged children.</p> Trial registration number and date of registration <p>2021/605, 09.09.2021.</p>