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Background: In at least 15 % of dilated urinary tracts, diuresis renography fails to assess the presence or absence of urinary obstruction., Objective: To determine the shortcomings of (99 m)Tc-DTPA frusemide diuresis renography by reference to pressure flow studies., Materials and Methods: Thirty-four patients, aged 1 month to 20 years, with questionable obstruction were evaluated by diuresis renography and pressure flow studies (the Whitaker test) as the reference method during the same short period of time. Discrepancies were analysed., Results: In patients with type I or IIIa renographic response, pressure flow studies never led to any change in management. Poor function, major dilatation and prior surgery were found to be risk factors of inaccurately obstructive pattern (type II) on renography (n = 6). In patients with type IIIb response, pressure flow studies could show low-grade (n = 3) or intermittent obstruction (n = 2). Intermittent obstruction was also demonstrated in two patients with type II response., Conclusion: In patients with risk factors, type II response was sometimes inaccurate, and urodynamic evaluation showed absence of obstruction and led to conservative management. Type IIIb response should be considered equivocal rather than partially obstructive, and pressure flow studies could be considered in such patients.