Peutz-Jeghers syndrome (PJS, MIM 175,2000) is a disease of autosomal dominant inheritance that is characterised by hamartomatous gastrointestinal polyps and mucocutaneous pigmentation. In addition to problems such as intussusception, PJS predisposes to cancers of several sites. The unusual combination of clinical features makes the identification of the defect underlying PJS particularly interesting. Recently, the PJS gene has been mapped to chromosome 19p13.