background: to determine the usefulness of Doppler ultrasound measurement of resistive index (RI) in differentiating obstructive from non-obstructive hydronephrosis in children. Methods: From August 2011 to November 2012, renal Doppler assessments of the intra-renal renal arteries were performed on 16 children (19 kidneys) with congenital hydronephrosis. the independent t-test was used to assess for significant difference in RI values between those with obstructive hydronephrosis (6 kidneys) and those with non-obstructive hydronephrosis (13 kidneys) as determined by dynamic renal scintigraphy. the assessor was blinded to the clinical findings and scintigraphy results. Results: RI was significantly different between obstructive and non-obstructive hydronephrosis. Obstructive hydronephrosis returned higher RI values, with mean RI of 0.78. Mean RI in non-obstructive hydronephrosis was 0.70, and the difference was significant (p <0.05). the sensitivity and specificity of Doppler ultrasound were 100% and 53% respectively. conclusion: Doppler ultrasound measurement of resistive index is useful in differentiating obstructive from nonobstructive hydronephrosis and provides an alternative non-ionizing investigation other than dynamic renal scintigraphy.