The Dutch national practice guideline 'Diagnosis and treatment of inflammatory bowel diseases (IBD) in adults' describes the multidisciplinary approach for adult patients with (suspected) IBD, recommended following analysis of the literature according to the principles of evidence based guideline development. The symptoms on first presentation of a patient with IBD are mainly connected with the localisation and severity of the disease and less with the resulting diagnosis 'Crohn's disease' or 'ulcerative colitis'. There is no test by which the diseases can be distinguished with certainty. Clinical course, ileocolonoscopy and histopathological investigation following biopsy form the 'gold standard' for diagnosis of IBD. The final diagnostic step is disease assessment according to the Montreal classification in order to enable unambiguous communication with medical professionals. The first aim of treatment is to treat and stabilise active disease (induction therapy); at the same time maintenance therapy is initiated. A step-up approach is recommended for both treatment aims. Surgical intervention is indicated if the medical treatment is ineffective, in case of intractable gastrointestinal bleeding, in clinically significant gastrointestinal stenosis due to fibrotic scar tissue, or if complications of the inflammation occur such as abscess, peritonitis, or complicated fistula formation. Nutrition and diet do not play a primary therapeutic role in treatment of adult patients with IBD. However, supportive nutritional care is warranted. Probiotics have a demonstrable effect in preventing pouchitis, but not in the treatment of IBD. Alternative medicine has no role to play in the treatment of IBD. The risk of developing colorectal carcinoma is slightly elevated in IBD patients. Therefore, endoscopic surveillance strategies, aimed at early detection of dysplasia, is indicated according to a schedule in which the frequency increases according to the time elapsed since first clinical signs of IBD.