We report the results of a two-part study examining the incidence of urinary tract infection during the first year of life. In the first part of the investigation, we reviewed the occurrence of urinary tract infection in a cohort of 3,924 infants born at our institution during a 4-year period. Infection developed in 16 infants (0.41%). The incidence of urinary tract infection in noncircumcised males was greater than the incidence in both female (P < .004) and circumcised male (P < .001) infants. In the second part of the study, we explored the frequency of urinary tract infection in all infants born in US Army hospitals, worldwide, over a 10-year period. There were 422,328 infants born in army facilities during this time period. Subsequent hospitalization for urinary tract infection occurred for 1,825 (0.43%) infants during the first year of life. Overall, there was no male preponderance for infections in early infancy compared with females. After an equivalent incidence during the first month of life, female infants had significantly more infections than did male infants (P < .001). However, noncircumcised male infants had a higher incidence of urinary tract infection than female infants (P < .001). Additionally, noncircumcised male infants had a tenfold greater incidence of infection than circumcised male infants (P < .001). There was a significant decrease in the circumcision frequency rate during the 10-year study period (from 85.4% to 73.9%, P < .001). As the number of circumcisions decreased, there was a concomitant increase in the overall number of urinary tract infections in males (P <.02). A reduced incidence of infection may be at least one medical benefit of routine neonatal circumcision.