The Finnish Patient Data Repository is a nationwide electronic health record (EHR) system collecting patient data from all healthcare providers. The usefulness of the large amount of data stored in the system depends on the underlying data structures, and thus a solid understanding of these structures is in focus in further development of the data repository. This study seeks to improve that understanding by a systematic literature review. The review takes the physician's perspective to the use and usefulness of the data structures. The articles included in this review study data structures intended to be used in the actual care process. Secondary use and nursing aspects have been covered in separate reviews. After applying the predefined inclusion and exclusion criteria only 40 articles were included in the review. The research on widespread systems in everyday use was especially scarce, most studies concentrated on narrow fields. Majority of these studies were primarily developed for specialist use in secondary care units. Most structures or applications studied were at an early stage of development. In many applications the use of structured data was found to improve the completeness of the documented data and facilitate its automated use. However, there seem to be some applications where narrative text cannot be easily replaced by structured data. Usability results regarding structured representation were conflicting. The scattered nature and paucity of research hinders the generalizability of the findings, and from the system design or implementation point of view the practical value of the scientific literature reviewed is limited.