We reviewed all available chest X-rays of 95 patients with hereditary hemorrhagic telangiectasia (HHT). The diagnosis of pulmonary arteriovenous fistula (PF) had previously been made in 13 patients, nine of whom had been operated on. Another three cases were found in the review. The 16 patients with HHT and PF came from eight families, one of which contributed seven patients. Median observation time between the first and the latest chest X-ray examination was 11 years (range 1/2-35). Growth of the PF was seen in four patients and spontaneous regression in one. Four of the 16 patients with PF had symptoms consistent with cerebral embolism, while only two of the 79 patients without PF had such symptoms. This study is part of an epidemiological investigation of HHT--to our knowledge not carried out before. The calculated period prevalence of simultaneous HHT and PF in the decade 1964-74 in the county of Fyn (429 207 inhabitants) was 2.6 per 100 000.