The primary diagnosis of chronic inflammatory bowel disease (Crohn's disease, ulcerative colitis) is performed by standardized procedures in specialized Gastroenterology Departments or Ambulances. For the assessment of disease activity the clinical presentation of the patient is most important. This is also true for the indication for surgical interventions. In certain instances laboratory markers, endoscopic and histologic examinations, ultrasound, X-ray, and cross-sectional imaging like computed tomography (CT) or magnetic resonance imaging (MRI) give important additional informations. Depending on the clinical situation surgeons and gastroenterologists decide on the most useful technical examinations for planning the operative strategy. After surgery, diagnostic procedures focus on disease progression and complications. Disturbances of intestinal function as consequence of the operation have also to be considered in the routine diagnostic program.