Vesicoureteral reflux (VUR) after a first episode of urinary tract infection (UTI) is apparently diagnosed much more frequently (25%-40%) in children than in neonates. The aims of the study were to determine the actual rate of VUR in neonates with UTI and to define the clinical clues to its diagnosis. The study sample included term infants with a diagnosis of UTI during their first month of life who were seen in this hospital between January 1997 and May 1999. All infants underwent complete diagnostic work-up (renal ultrasound and voiding cystourethrography [VCUG]). The medical files were reviewed for patient sex, age at UTI diagnosis, laboratory findings (including causative pathogen), and ultrasonographic findings. These parameters were correlated with the finding of VUR on VCUG. Sixty-four neonates (55 males, 9 females) with UTI were included in this study. UTI was 6 times more common in males than females, although the incidence of VUR was equal between the sexes (about 20%). The presence of VUR was associated with a significantly younger age at presentation of UTI (11.4+/-4 vs 16.9+/-6.6 days, p<0.01). VUR was diagnosed at a fourfold higher rate in neonates with Klebsiella-induced UTI compared to those with E. Coli-UTI. In 80% of those with significantly abnormal ultrasonographic findings VUR was found on VCUG. Jaundice was noted at UTI diagnosis 3 times more often in infants with VUR, and elevated creatinine level, 2.5 times more often.