Occult visceral arterio-venous malformations (AVMs) may be a constant threat to patients suffering from hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber syndrome (M. ROW). HHT patients predominantly become symptomatic through chronic, recurrent epistaxis, a symptom that can alert physicians at an early stage of the disease. The purpose of this study was to investigate whether occult, visceral arterio-venous malformations could be detected by screening imaging studies in patients suffering from HHT. In a comprehensive diagnostic study, Rendu-Osler-Weber patients were examined for potential visceral arterio-venous malformations by physical examination and non-invasive imaging techniques. The Department of Otolaryngology of the Philipps University of Marburg is a major referral center and coordinated the screening procedures. Thirty-five individuals with the presumed diagnosis of HHT gave informed consent to the screening investigations. Eighteen of 35 individuals were found to suffer from visceral vascular malformations; most of the AVMs were diagnosed in the lung, but also the liver, spleen, brain and eyes were affected. Six patients could be treated preventively by arterial embolization for AVMs of the lung, liver and brain. Comprehensive screening for occult AVMs in HHT patients seems to be justified to avert potential complications in this group of patients.