The purpose of this study was to evaluate the accuracy and reliability of duplex Doppler ultrasound (US) and computerized tomography (CT) in staging patients with renal cell carcinoma (RCC). Sixty-six patients were evaluated pre-operatively with duplex Doppler ultrasound and CT. The results were compared with the surgical and histopathological findings. T stage was determined correctly with duplex Doppler US and CT in 56 and 50 cases respectively. In 4 patients with nodal disease duplex Doppler US was correct in 2 patients, 1 was false positive. With CT, 3 patients were staged correctly and 3 were false positive. Of the 14 patients with vascular tumour thrombi, 13 were staged correctly with duplex Doppler US and 12 with CT scan. False positive vascular tumour invasion was seen only with CT in 4 cases. Based on these results we conclude that duplex Doppler US is at least as accurate as CT scanning in the staging of RCC. Also in patients with renal or caval thrombi, duplex Doppler US is highly accurate in establishing the diagnosis and in the determination of the extent of the thrombus.