Aim: Few retrospective studies have evaluated infants with hypertrophic pyloric stenosis (HPS) for associated urological anomalies. They have led to contradictory conclusions. The aim of this study was to evaluate the incidence of urinary tract anomalies in infants with HPS and to establish the clinical significance of this association. Methods: One hundred and twenty-two infants (100 boys) who underwent pyloromyotomy between 1992 and 2002 were prospectively evaluated. Screening ultrasound (Us) of the urinary tract was performed in 107 infants, while 15 did not attend their ultrasound appointment. Results: Renal ultrasound was abnormal in 4 (4%) of 107 screened patients with HPS. Three patients were found to have mild hydronephrosis and, in one patient, a small, normal kidney was detected. Two patients with hydronephrosis had Us follow-up and the third patient underwent Tc-99 mercaptoacetyl triglycine (MAG 3) scan. In all three patients, the hydronephrosis resolved completely on follow-up scan. Conclusion: The incidence of abnormal renal ultrasound in children with HPS is similar to the reported incidence of 3-6%determined with routine ultrasound screening of healthy newborns. The abnormalities detected were not clinically relevant and did not require surgical intervention. We do not recommend screening of the urinary tract in infants with HPS. Aim: Few retrospective studies have evaluated infants with hypertrophic pyloric stenosis (HPS) for associated urological anomalies. The aim of this study was to evaluate the incidence of urinary tract anomalies in infants with HPS and to establish the clinical Significance of this association. Methods: One hundred and twenty-two infants (100 boys) who underwent pyloromyotomy between 1992 and 2002 were prospectively evaluated. Screening ultrasound (Us) of the urinary tract was performed in 107 infants, while 15 did not attend their Three patients were found to have mild hydronephrosis and, in one patient, a small, normal kidney was detected. Two patients with hydronephrosis had Us (4%) of 107 screened patients with HPS. follow-up and the third patient underwent Tc-99 mercaptoacetyl triglycine (MAG 3) scan. In all three patients, the hydronephrosis resolved completely on follow Conclusion: The incidence of abnormal renal ultrasound in children with HPS is similar to the reported incidence of 3-6% determined with routine ultrasound screening of healthy newborns. The abnormalities were detected in not clinically relevant and did not require surgical intervention. We do not recommend screening of the urinary tract in infants with HPS.