This thesis deals with most common clinically manifested diseases of the colon in dogs. Besides that, this thesis deal also with the endoscopic diagnostics of those upper mentioned diseases, as well with other types of diagnostics. Most common diseases of colon are: accute colitis, infectious diseases (bacterial, viral and parasitic), inflammatory bowel disease, irritable bowel syndrome, coprostasis, intussusception and tumors. Their etiology, clinical examination, diagnostics with endoscopy, prognosis and treatment possibilities are well presented in this thesis. Most of these disorders and illnesses can be treated very successfully if noticed on time. The diagnosis of colon diseases is based on a detailed history, clinical axamination, laboratory blood tests, X-ray (native or contrast), CT and ultrasound examination of the abdomen and endoscopic examination with biopsy and pathohistological examination. An essential part of the diagnosis of colon disease includes stool tests for parasites, and sometimes bacteriological tests and tests for bacterial toxins. The method of treatment and choice of drugs depends on the underlying disease of the colon. Depending on the diagnosis and severity of the disease it may include symptomatic therapy, diet, probiotics, antiparasitic drugs, antimicrobial drugs and anti-inflammatory and immunosuppressive drugs. In the case of neoplasia, therapy is based on surgical excision of the tumor and cytostatic protocols. The prognosis for most acute and even some chronic colon diseases is good, while for more severe chronic diseases it is poor or unpredictable, especially when it comes to more severe cases of inflammatory bowel disease or neoplasia.