Among colorectal cancer patients, about 20% have a family history of colorectal cancer, and the family history of 5-10% of them is in accordance with Mendel’s law, i.e., the characteristics of autosomal dominant inheritance. Clinically, based on the presence or absence of polyposis, hereditary colorectal cancer can be divided into two major categories: hereditary polyposis and hereditary non-polyposis colorectal cancer. Hereditary polyposis can be subdivided into hereditary adenomatous polyposis, which includes familial adenomatosis FAP and Turcot syndrome, and hereditary dysplasia polyposis, which includes Peutz-Jeghers syndrome and familial juvenile polyposis. The 18-year-old patient had familial adenomatous polyposis, a group of autosomal dominant syndromes characterized by multiple adenomas in the colorectum, which accounts for approximately 1% of colorectal cancers. The clinical features are adenomatous polyps and microadenomas that spread throughout the colon and number more than 100. Adenomas begin to appear in patients in their teens, and if left untreated, almost 100% of patients will develop colorectal cancer by age 40. Because of the large number of adenomas in FAP patients, it is not possible to remove all adenomas through colonoscopy, and because 100% of patients will eventually develop colorectal cancer, surgical removal of the entire colon is currently the most effective means of preventing adenoma carcinoma in FAP patients. Thus, it seems that the prevention of resection of the large intestine in this small patient is necessary. Does the absence of family history mean that I cannot get hereditary colorectal cancer? 60%-70% of familial adenoma patients have a clear family history of colorectal cancer or polyps, carrying genetic mutations inherited from previous generations; another 30% of FAP patients are new cases with no family history, and these patients are often not found to be FAP patients until they develop polyps or cancerous symptoms. The occurrence of bowel cancer in this group of patients is related to the mutation of the gene. Therefore, young people should pay great attention when they have symptoms such as blood in stool, change of stool habit, abdominal pain, anemia, and weight loss. Colonoscopy or barium examination: When colonoscopy or barium enema examination reveals hundreds of polyps in the colorectum, the possibility of FAP should be considered first. Colonoscopy to understand the distribution of polyps, biopsy of polyps and suspicious cancerous lesions, and removal of some polyps can alleviate some patients’ symptoms while clarifying the diagnosis.