Various extraintestinal manifestations may occur in juvenile polyposis, but hereditary hemorrhagic telangiectasia has rarely been reported in this type of polyposis. The authors treated a 14-year-old girl with rectal bleeding and anemia who had multiple polyps of the colorectum. Large polyps were removed and histologically diagnosed as juvenile polyps. She was later diagnosed as having telangiectasia of the skin, and arteriovenous malformations in the lung and in the liver, all of which were compatible with the diagnosis of hereditary hemorrhagic telangiectasia. At age 32, she had multiple ulcers in the ileum and in the colon. The coexistence of juvenile polyposis and hereditary hemorrhagic telangiectasia may be a clue for the understanding of the histopathogenesis of juvenile polyposis.