Colorectal cancer (CRC) is the 2nd most common cancer in Germany (incidence 70,000 individuals each year). In 20–30% of all cases, a positive familial history is present, and in 2–5% there is a monogenetic background. The most common form of hereditary CRC is hereditary nonpolyposis colorectal cancer (HNPCC), also called Lynch syndrome. Less frequent are familial adenomatous polyposis coli (FAP) and the hamartomatous polyposis syndromes (Peutz–Jeghers syndrome and juvenile polyposis syndrome). Multiple colorectal adenoma syndrome (MAP) is inherited in an autosomal recessive manner and is an important differential diagnosis for Lynch syndrome and attenuated FAP. In all of these syndromes, individuals have a higher risk of developing CRC as well as a broad spectrum of malignancies outside the colorectum. With the identification of genetic background associated with hereditary CRC, at-risk persons now have the chance to know their individual risk before they develop malignancies.