The relevance of the research on this topic is conditioned by the fact that duodenal ulcer is a serious problem, which is addressed by the efforts of a huge number of gastroenterologists around the world, and therefore it is necessary to comprehensively study as much as possible modern theoretical information on this issue. In this regard, this study is aimed at the fullest possible disclosure of the theory accumulated to date regarding information about duodenal ulcer and its complications, namely: bleeding, perforation, penetration. The leading approach to the study of this issue is an empirical method that makes it possible, in combination with a number of theoretical methods, to conduct a comprehensive comparative analysis of the existing array of scientific literature, which, most importantly, is relevant to the present time, and, possibly, to identify certain new approaches regarding various aspects in issues related to duodenal ulcer and its complications. This paper presents the results of a theoretical review of information about duodenal ulcer and its complications that has appeared in the literature recently, and covers various aspects related to this disease, with much attention paid to the issues of complications.