Irrespective of whether it is present at admission1 or at a later stage,3, 4, 8, 10 diaphragm dysfunction is a marker of illness severity and of poor prognosis. At the early stage of critical illness, diaphragm dysfunction is analogous to any other form of organ dysfunction and its presence is associated with higher mortality.1 To what extent diaphragm dysfunction can contribute to a poor prognosis has not been elucidated. Importantly, diaphragm dysfunction can improve despite exposure to mechanical ventilation.19 Nevertheless, the time of course and the determinants of the recovery need to be clarified in further studies. At the time of liberation from mechanical ventilation, diaphragm function is an important determinant of weaning outcome. In isolation, diaphragm dysfunction is usually not sufficient to precipitate respiratory failure and weaning failure, but in the presence of high ventilatory demands or deteriorating respiratory mechanics it may rapidly result in weaning or extubation failure. In the study by Kim and co-workers who used ultrasound to detect diaphragm dysfunction, diaphragm dysfunction was associated with a longer weaning time (401 hours vs. 90 hours, p<0.01).10 However, diaphragm dysfunction can also be present in patients who are successfully liberated from ventilation.8, 20 Of note, some studies indicate that a substantial proportion of patients (up to 44%) can be successfully weaned from the ventilator despite having diaphragm dysfunction.1, 7 is is not surprising as many patients with chronic diaphragm dysfunction do not require mechanical ventilation. While diaphragm dysfunction might limit exercise capacity, the clinical consequences of diaphragm dysfunction in successfully liberated patients is uncertain. However, the impact of respiratory muscles dysfunction (not specifically the diaphragm) aer critical illness may be of importance since it is associated with worse long-term outcomes.