Introduction: Crohn's disease is a well-characterized disease, and treatment is carried out according to international guidelines. Despite this, the disease often show an individual, unpredictable course, and more than half of patients experience significant complications of the disease. Endoscopy is important for the assessment of disease dissemination and severity of Crohn's disease, which is complemented by biochemical and clinical indices, including CDAI or Simple Index (SI) (Harwey-Bradshaw), which is internationally recognized. By CDAI, there is shown a good correlation with the biochemical activity markers such as CRP, and serum albumin, and in practice the simplified version (SI). Is often used.