Renal artery stenosis (RAS) is a cause of secondary hypertension and renal insufficiency, most commonly due to atherosclerosis or fibromuscular dysplasia. Doppler ultrasound evaluation includes measurement of peak systolic velocity at the renal artery origin (PSV >180–200 cm/s is suspicious), the renal-to-aortic velocity ratio (>3.5 is significant), and intrarenal waveform analysis including acceleration time and resistive index. RAS evaluation is technically demanding and requires careful scanning of the main renal arteries and intrarenal segmental vessels.