Cutaneous findings are not uncommonly a concomitant finding in patients afflicted with gastrointestinal (GI) diseases. The dermatologic manifestations may precede clinically evident GI disease. Part I of this 2-part CME review focuses on dermatologic findings as they relate to hereditary and nonhereditary polyposis disorders and paraneoplastic disorders. A number of hereditary GI disorders have an increased risk of colorectal carcinomas. These disorders include familial adenomatous polyposis, Peutz–Jeghers syndrome, and juvenile polyposis syndrome. Each disease has its own cutaneous signature that aids dermatologists in the early diagnosis and detection of hereditary GI malignancy. These disease processes are associated with particular gene mutations that can be used in screening and to guide additional genetic counseling. In addition, there is a group of hamartomatous syndromes, some of which are associated with phosphatase and tensin homolog (PTEN) gene mutations, which present with concurrent skin findings. These include Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, and Cronkhite–Canada syndrome. Finally, paraneoplastic disorders are another subcategory of GI diseases associated with cutaneous manifestations, including malignant acanthosis nigricans, Leser–Trélat sign, tylosis, Plummer–Vinson syndrome, necrolytic migratory erythema, perianal extramammary Paget disease, carcinoid syndrome, paraneoplastic dermatomyositis, and paraneoplastic pemphigus. Each of these disease processes have been shown to be associated with an increased risk of GI malignancy. This underscores the important role of dermatologists in the diagnosis, detection, monitoring, and treatment of these disorders while consulting and interacting with their GI colleagues.