Recurrent episodes of cutaneous and subcutaneous ulcers, especially in the oral cavity, represent a high psychological and painful burden for the patient. If there in addition are symptoms of arthralgia and/or colitis, an autoimmune disease with vasculitis, particularly a Morbus Behçet has to be considered as a possible differential diagnosis. The therapy therefore would be an immunosuppressive one. Also a wide immunologic diagnostic process has to be started. Furthermore, a chronic inflammatory bowel disease has to be excluded by colonoscopic biopsy. An infectious etiology of the symptoms (viral/bacterial/parasitic) should be investigated by microbiological and laboratory tests. A thrush or a herpes-infection caused by immunosuppression (toxic or due to illness) has to be considered as a further differential diagnosis. Also a precise medical and drug history is very important because of possible toxic adverse effects. Until confirmation of a final diagnosis, only a symptomatic analgetic or antifungal or antiviral therapy in case of a positive thrush or herpes culture respectively should be initiated with respect to the very different kinds of treatment of the diseases included in the differential diagnosis.