Transoesophageal Doppler (TED) is a minimally invasive, quick and easy technique to assess descending aortic blood flow in critically ill patients. The frequency shift between emitted ultrasound and ultrasound scattered back to the probe by moving erythrocytes, enables flow velocity to be determined according to the Doppler principle. Using the velocity-time integral, flow velocity can be translated to the stroke volume of the descending aorta, from which the left ventricular stroke volume can be estimated. Moreover, TED technology measures additional haemodynamic parameters that may facilitate assessment of preload, afterload and myocardial contractility. Several validation studies have compared TED-derived cardiac output (CO) to reference methods and underline the usefulness of TED as a trend-monitoring device to follow changes of CO over time. Clinical use of TED monitoring in intensive care units (ICU), either as a substitute or supplement to other monitoring devices, has repeatedly been reported to yield useful data for the assessment and treatment of critically ill patients. Randomized controlled studies suggest improvements in outcome (less postoperative morbidity and shorter length of hospital stay) in the surgical patient population when TED is used to guide volume replacement intraoperatively or postoperatively on the ICU. However, data to support its usefulness in the non-surgical critically ill population are limited and also the usefulness of TED to guide vasoactive or inotropic therapy needs to be further determined. In this paper, we review current knowledge on technical and clinical aspects of the TED method and focus on its role in haemodynamic monitoring on the ICU. © 2010, Nederlandse Vereniging voor Intensive Care.