The diagnostic value of pulsed Doppler sonography for the detection of renal artery stenosis was questioned by recent studies. Until now, the diagnostic value of colour-coded Doppler sonography of the renal arteries is not clearly defined in relation to pulsed Doppler. This study deals with specific problems of colour-coded Doppler sonography in the examination of the renal arteries. Because of basic technical principles of colour-coded Doppler sonography a stenosis can be imitated especially at the origin of the right renal artery by using a ventral approach to the vessel. This pseudo-stenosis is due to a change of colour similar to an aliasing-phenomenon in a curved vessel. In order to avoid false positive results, a laterodorsal approach to the vessel should be applied additionally. A spectral waveform should be also registered routinely.