We aimed to evaluate the association of body weight status and increased risk for urinary tract infection (UTI) in pre-school children using the Korean National Health Screening (NHS) dataset.  nationwide population-based study was conducted using data from the NHS for infants and children and from the National Health Insurance Service. A sample cohort was first selected from the 2014 and 2015 NHS for infants and children aged from 4 months to 6 years, and followed up though 2017. Subjects were classified as underweight, normal reference group, overweight, or obese based on weight-for-age (< 2 years) or body mass index (≥ 2 years). The hazard ratios (HRs) and 95% confidence interval (CI) for developing UTI, cystitis, and acute pyelonephritis (APN) were calculated using a Cox proportional hazard model Of 1,653,106 infants and children obtained from the sample cohort, 94,185 patients (5.7%) developed UTI during follow-up of 37.6 months. Underweight, overweight or obesity had a higher risk of UTI, cystitis or APN, compared to the normal reference group, after adjusting for age, sex, birth weight, and prematurity. Under 2 years of age, overweight and obese female infants showed a higher risk of APN relative to control girls (HR 1.18 [1.07-1.29], 1.23 [1.10-1.37], respectively). Between 2 and 6 years of ages, the HR of APN in underweight boys relative to control boys was 1.46 (95% CI 1.03-2.07) and that in obese girls was 1.41 (95% CI 1.13-1.75) after adjusting for age, birth weight, and prematurity. Underweight, overweight, and obesity may be associated with increased incidence of UTI in infants and children.