Lynch sindrome is the most common form of hereditary nonpolyposis colorectal cancer. In its core is elevated risk for developing colon, endometrial, ovarian and stomach carcinoma while risk for developing other types of carcinomas is lower, but still exists. There are two types of Lynch sindrom classified considering the presence of extracolonic carcinomas. High risk for developing tumors is a direct consequence of mutations in mismatch repair genes. Cell's ability to repair DNA has been compromised which results in accumulation of point mutations and microsatellite instability. Inheritance of Lynch syndrome is autosomal dominant which means one mutated allele is enough to cause elevation of risk for developing carcinoma and it can be inherited by both parents. Risk for inheritence of mutated allele in an offspring is 50%. Being familiar with Lynch sindrome genetics makes it possible for patients to be screened, checked up regularly, diagnosed early and treated properly. Since Lynch syndrome is a form of hereditary nonpolyposis colorectal cancer, Amsterdam criteria I, II and revised Bethesda guidlines can be used in diagnosis. These criteria and guidelines help to determine when is necessary to test tumor tissue for mutations and when to perform genetic tests on patients and their family members using their blood samples. Although protocols of chemotherapy used in treatment are not always succesfull, there is hope for patients with Lynch syndrome. In development are monoclonal antibodies that are succesful in targeting tumors caused by microsatellite instability. That shows how important it is to know about genetic basis of syndromes we treat.