Diagnostic procedures in inflammatory bowel diseases (IBD) serve to secure the diagnosis and to optimize treatment. Upon initial diagnosis endoscopy up to the terminal ileum is mandatory including multiple step biopsies. When diagnostic guidelines are followed and adequate clinical information is available, IBD will be correctly classified in about 80 to 90% of cases upon first examination. In contrast endoscopic studies are only of limited value in monitoring treatment. The decision if and when to perform endoscopy during exacerbation of disease must be an individual one. When disease activity is evaluated, a distinction must be made between degree of activity as reflected by laboratory parameters and severity of illness as reflected by the clinical presentation with abdominal complaints, fistulas, abscesses, etc. Distinct activity indices are useful in clinical studies to obtain an objective evaluation of activity and severity of disease. At clinical routine visits questions should not only concern the basic illness but also ask for quality of life and psychosocial status. Only a small number of laboratory tests are needed for basic diagnosis and follow-up. A small bowel enteroclysis should always be performed upon primary diagnosis of Crohn's disease and during the course of disease when there is suspicion of small-bowel involvement. Double contrast barium enema should be limited to special indications as incomplete colonoscopy e.g. due to stenosis or suspected fistula. Sonography is the primary investigation when complications are suspected. CT is useful as an adjunct or when the afore mentioned methods do not show clear findings. NMR is the procedure of choice for detection of pararectal fistulas and abscesses. Transrectal endosonography is comparably good but limited to the experience of the investigators and by patient's tolerability.