Rapidity of response to treatments in inflammatory bowel diseases is now considered a field of major interest, due to the importance of achieving the highest benefit in the shortest possible time, in order to favor a fast backward step to normal life. There are no previous studies specifically designed to evaluate the rapidity of response to adalimumab therapy in patients with active Crohn's disease. Studies on rapidity of onset of response to adalimumab have, on the other hand, been performed in other diseases such as rheumatoid arthritis (Efficacy of HUMIRA in Subjects With Active Rheumatoid Arthritis HERO study, Wolfe et al, 2006). This trial will assess the clinical responses occurring earlier than in week 1. This is an open label, one arm, prospective, multicenter, phase IV clinical trial.