Diseases of small intestine remain virtually unknown to the general practitioners despite the high prevalence of this gastroenterological pathology. The difficulties encountered in diagnostics of small intestine pathology are attributable to the peculiarities of localization of the small intestine that make it almost inaccessible for the investigation. Moreover, these disorders have clinical symptoms that are very similar to the manifestations of other diseases. The common clinical syndromes of small intestine pathology include chronic diarrhea, malabsorption syndrome, and exudative enteropathy syndrome. Correct diagnosis of these disorders is possible on condition of the comprehensive approach with the application of laboratory and instrumental methods highly informative for a given disease. Of special importance for correct diagnostics of intestine pathology is the thorough collection of subjective complaints, analysis of medical histories, and objective investigations. The immunological methods play the leading role in the laboratory studies because they allow to recognize the presence of the disease before its clinical manifestations become apparent. The endoscopic techniques provide the efficacious tool for diagnostics of small intestine pathology especially if they are applied in combination with the collection of biopsies of intestinal mucosa and their histological studies. The up-to-date videoendoscopic techniques are successfully employed to detect oncological diseases of the small intestine and thereby facilitate their early diagnostics.