Because of technical and practical difficulties in relation to increased body size, haemodynamic monitoring of morbidly obese critically ill patients (i.e. body mass index ≥40 kg÷m2) may be challenging. Obese and non-obese patients are not so different with respect to haemodynamic monitoring and goals. The critical care physician, however, should be aware of the basic principles of the monitoring tools used. The theoretical assumptions and calculations of these tools could be invalid because of the high body weight and fat distribution. Although the method of assessing haemodynamic data may be more complex in morbidly obese patients, its interpretation should not be different from that in non-obese patients. Indeed, when indexed for body surface area or (predicted) lean body mass, reliable haemodynamic data are comparable etween obese and non-obese individuals.