A variety of diagnostic methods provide the necessary rational basis for diagnosis, assessment of disease activity and exclusion of possible complications for patients with inflammatory bowel disease (IBD).Currently, a wide range of diagnostic methods is available and easily accessible. The clinical use of all these different methods is inherently possible. As there is no reference test for either diagnosis or monitoring of IBD, diagnostic techniques must be selected, applied and interpreted in an appropriate clinical context. The objective is to evaluate the clinical, laboratory and imaging techniques including ultrasound and endoscopy in different clinical situations.In addition to clinical parameters, fecal calprotectin and abdominal ultrasound are helpful tools to assess the inflammatory activity. In patients with high inflammatory activity, a routine endoscopy is not beneficial. At best, endoscopy can be performed to document the extent of mucosal inflammation before initiating an intensified immunosuppressive therapy. Knowledge and experience in the management and treatment of IBD complications are critical in providing a rational use of specific diagnostic methods.As a basic principle, the critical evaluation of diagnostic methods in patients with IBD is of great importance. Specific clinical situations require specific diagnostic techniques. Every diagnostic method performed should have a purpose.