Isotope renography is a commonly used investigation for the detection of renal artery stenosis (RAS) in hypertensive patients, although its predictive accuracy is poor in an unselected population with a low prevalence of RAS. The aim of the present study was to identify characteristics of hypertensive patients that raise the clinical suspicion of underlying RAS, and which are predictive of an abnormal isotope renogram. The characteristics of 75 patients who had undergone either conventional or ACE-inhibitor-enhanced renography were retrospectively assessed and correlated with the renogram results. The presence of a raised serum creatinine, severe systolic hypertension at presentation and the requirement for triple drug therapy best predicted abnormalities on renography. However, it would appear that the false-positive rate of this investigation is high and its predictive accuracy is poor even in a highly selected group of patients. We conclude that isotope renography is of no practical value in the screening of hypertensive patients for RAS. Renal angiography remains the investigation of choice.