Purpose:To determine the value of duplex Dopplersonography in the diagnosis of acute urinaryobstruction.Materials and methods:In 46 healthy individuals and 42 patients withurinary obstruction confirmed by intravenousurography, 176 kidneys were examined withduplex Doppler sonography. The meanintra-arterial resistive index value and thedifference of mean resistive index valuesbetween both kidneys were determined for eachperson. Resistive index and delta resistiveindex values were compared with urographicfindings in the 42 patients.Results:In the 46 healthy individuals, the meanresistive index and delta resistive indexvalues were 0.59 ± 0.05 and 0.03 ±0.01. In the 14 patients with complete urinaryobstruction, these values were 0.70 ± 0.06and 0.09 ± 0.02, whereas in the 28 patientswith partial urinary obstruction, these valueswere 0.64 ± 0.06 and 0.03 ± 0.05.Urographic findings and duplex Dopplersonography were correlated in the 42 patients,with a resistive index = 0.65 and deltaresistive index = 0.05 as discriminatorythresholds for obstruction. In patients withcomplete obstruction, the diagnosticsensitivity of these values was 64% and 100%with a specificity of 82% and 89%,respectively. In patients with partialobstruction, the sensitivity of these valueswas 54% and 46% with a specificity of 82%and 89%, with respect to the control group ofhealthy individuals.Conclusion:Delta resistive index is a very sensitive andspecific parameter in the sonographic diagnosisof complete urinary obstruction but insensitivein partial urinary obstruction. Duplex Dopplersonography is recommended in cases whereintravenous urography is contraindicated.