Doppler sonographic findings were correlated with symptoms and intravenous urographic findings in 31 patients with unilateral renal obstruction and in 30 control subjects. No significant correlation was found between resistive index and symptom duration or between resistive index and pelvicalyceal opacification time on intravenous urography. With a cutoff resistive index of 0.7, the sensitivity was 19.3% in diagnosing unilateral obstruction; however, it was 80% in the subgroup with acute symptoms and severely delayed pelvicalyceal opacification time. Doppler sonography has very low sensitivity in diagnosing unilateral renal obstruction, but it may be useful when the obstruction is acute and severe.