PURPOSE OF THE REVIEW: This paper will review the evidence for mitochondrial dysfunction in critical illness, describe the mechanisms which lead to multiple organ failure, and detail the implications of this pathophysiologic process on nutritional therapy. RECENT FINDINGS: Mitochondria are particularly sensitive to increased oxidative stress in critical illness. The functional and structural abnormalities which occur in this organelle contribute further to the excessive production of reactive oxygen species and the reduction in generation of adenosine triphosphate (ATP). To reduce metabolic demand, mitochondrial dysfunction develops (a process likened to hibernation), which helps sustain the life of the cell at a cost of organ system failure. Aggressive feeding in the early phases of critical illness might inappropriately increase demand at a time when ATP production is limited, further jeopardizing cell survival and potentiating the processes leading to multiple organ failure. Several potential therapies exist which would promote mitochondrial function in the intensive care setting through support of autophagy, antioxidant defense systems, and the biogenesis and recovery of the organelle itself. Nutritional therapy should supplement micronutrients required in the mitochondrial metabolic pathways and provide reduced delivery of macronutrients through slower advancement of feeding in the early phases of critical illness. A better understanding of mitochondrial dysfunction in the critically ill patient should lead to more innovative therapies in the future.