A 37-year-old female patient was admitted to our outpatient clinic because of abdominal pain and absence of stool for five days. A diagnosis of acute intermittent porphyria was made by determination of porphyrins in the urine and the stool, the absence of skin symptoms and the measurement of urosynthase activity. As triggering event we suspect a viral infection. Neurological and neuropsychiatric symptoms were absent.