LKB1 was first identified as the gene responsible for Peutz-Jeghers syndrome (PJS), a dominant disorder characterized by benign hamartomatous polyps in the gastrointestinal tract and mucocutaneous melanin pigmentation (Peutz, 1921; Jeghers et al., 1949; Hemminki et al., 1997). Here, STK11 is linked to Peutz-Jeghers syndrome.