Crohn's disease and ulcerative colitis are chronic relapsing inflammatory bowel diseases with extremely great variability in presentation and clinical course. For many decades, corticosteroids and aminosalicylates have been the mainstay of the treatment for both Crohn's disease and ulcerative colitis, for the induction and maintenance of remission, respectively. The main limiting factors for the repeated use of corticosteroids or the use as a maintenance treatment are the very high prevalence of systemic side effects, together with the possibility of developing dependency on and/or resistance to the drug, which are reported in more than one third of patients with inflammatory bowel disease. In the last decade, a number of corticosteroids with enhanced topical activity and low systemic activity have been developed. Among them, budesonide and beclomethasone dipropionate are the most used for the treatment of the inflammatory bowel diseases. Indeed, budesonide is the drug of choice for the treatment of ileo(-cecal) active Crohn's disease with mild-to-moderate activity, due to controlled ileal release. Budesonide foam and/or enemas are also efficacious in the treatment of left-sided/distal ulcerative colitis. Gastro-resistant, extended release tablets characterized by a multimatrix structure (i.e. MMX-budesonide), have also been developed to allow uniform release along the length of the colon. This paper reviews the mechanism-of-action, safety and efficacy of budesonide in the treatment of inflammatory bowel disease.