Objective: Adequate nutrition has an impact on outcome in critically ill patients. This descriptive literature search investigates whether there are differences in energy expenditure (EE) between specific subgroups of critically ill patients, including patients with sepsis, trauma, burns and cerebrovascular accidents. Also, we summarised specific factors which may influence EE, such as the use of sedation, body temperature and severity of illness. Design: A descriptive review of studies which have measured EE or oxygen consumption with indirect calorimetry in critically ill patients. Studies were retrieved by a systematic search of the Medline database, using search terms referring to the measurement (energy expenditure), the patient population in general (critically ill patients), and to the four specific subgroups (sepsis, trauma, burns, stroke). Results: EE in patients with sepsis, trauma and burns was increased (sepsis 102-198%; trauma 110-168%; burns 137-182%; stroke 149% for men and 120% for women) compared with reference values of EE in healthy individuals. Burn patients had the highest EE levels. There was no difference in EE between sepsis and trauma patients. Patients with a cerebrovascular accident had the lowest EE. Half of these patients had an EE that did not exceed EE levels in healthy adults. Use of sedation lowered EE whereas fever increased EE. Uncertainty persists whether treatment of stroke patients with hypothermia decreases EE. According to most studies, higher disease severity scores are associated with higher EE, but one study found that severity of illness is negatively correlated with EE in sepsis. Conclusions: Data for this review were limited, precluding definite conclusions. However, it is clear EE differs among critically ill patient populations. The use of a 'one size fits all' formula to estimate caloric need in the critically ill may not be appropriate in the design of studies on caloric need nor in patient care.