There are only a few published studies that demonstrate associations between life expectancy, severe comorbidities, and their complications in patients with hereditary hemorrhagic telangiectasia (HHT). Relatives of 73 deceased patients with suspected HHT completed a questionnaire about causes of death, and symptoms and comorbidities that the patients had developed. We compared the data for 55 cases where HHT had been clinically confirmed with the general population. Patients suffering from HHT lost, on average, 19 years (SD 11 years) of potential life compared to the general population. Among the deceased HHT patients, 35% (95% CI: 23–48%) died from sepsis, 26% (95% CI: 16–38%) from cardiac failure, 20% (95% CI: 9–28%) from a severe bleeding episode, and 13% (95% CI: 6–24%) from terminal cancer. Congestive heart failure (69%, 95% CI: 56–80%) and pulmonary hypertension (23%, 95% CI: 14–36%) were the main non-fatal comorbidities in patients with HHT. Patients with HHT appear to have a lower life expectancy than the general population. Sepsis and cardiac failure were the main causes of death. Optimized and targeted screening programs for the most frequent comorbidities followed by improved management of infectious complications may increase life expectancy.