The need for assessment of ureteric function in the patient with an obviousely dilated ureter has increased particularly with the added spectrum of asymptomatic patients presenting with hydronephrosis and hydroureter on antenatal and perinatal ultrasound. To assess the influence of ureteral status on kidney washout during Tc-DTPA diuretic renography, ureteral images were reviewed in 80 children referred for hydronephrosis. A scintigraphically abnormal ureter was defined as an intense and continuous image of > 10 min during diuretic renography. Out of them, a total of 16 nephroureter- al systems in 12 children with scintigraphically abnormal ureter were analyzed. A diuretic washout index using response half time (t1/2) by linear fitting after lasix injection, was determined on renal (Ktl/2) and ureteral (Utl/2) curves (diuretic renogram vs. diuretic ureterogram). Diuretic ureterogram curve patterns corresponding to normal (type I), obstructive (II) and non-obstructive (III) cases were described. Compared with X-ray data, diuretic renography was highly sensitive (88%) and specific (99%) for detecting any ureteral abnormality. Despite an obstructive Ktl/2 (> 20 min), no patient with an ahnormal ureter underwent therapy at the ureteropeivic junction because (he hydronephrosis regressed after surgery at the lower level. Our data indicate that the abnormal ureter findings during diuretic renography have to be recognized before therapy for children with hydeonephrosis.