Crohn's disease is frequently complicated by protein-calorie malnutrition. Four common clinical presentations of Crohn's disease include acute exacerbations or flares of disease, intestinal obstruction, fistulizing disease, and perianal disease. In this review, we examine the role of nutritional support in these clinical scenarios. Nutritional support is important for maintaining functional status and preventing loss of lean tissue. Determinants of lean-tissue loss include severity of underlying injury, baseline nutritional status, and duration of inadequate nutrition. One of the clinically useful measures of nutritional status is the nutritional risk index (NRI) defined on the basis of the serum albumin and weight loss. Nutritional support is important in severely malnourished patients (NRI < 83). Enteral nutrition is the route of choice, provided there are no contraindications to using the gastrointestinal tract. In acute exacerbations of Crohn's disease, enteral nutrition also has a role in the primary management of disease although it is not as effective as corticosteroids in inducing remission. The mechanisms are poorly understood and the most effective enteral formulation needs to be determined. Total parenteral nutrition is justified in severely malnourished Crohn's disease patients who are unable to tolerate enteral feeding or in whom enteral feeding is contraindicated. More clinical studies are needed on the assessment of malnutrition in Crohn's disease, the effects of nutritional management on functional status, and the timing of nutritional intervention.