The research has been conducted in the medical field and reflects the development of computer system. The computer system has been designed for arterial hypertension (high arterial blood pressure) differential diagnosis. It means that it is possible to determine with the computer system whether a patient has hypertension, and if it is found, then it is possible to determine the cause. The development of the computer system was based on the knowledge about hypertension diagnosis and treatment of cardiologists at the Research Institute of Cardiology of the University of Latvia and Pauls Stradins Clinical University Hospital. There are two tasks assigned for the diagnostic system and there are two stages made to reach these two tasks. The first task is the selection of hypertension patients or screening, implemented at the first stage. The second task is indicative differential diagnostics, which allows differentiating hypertension from 7 symptomatic arterial hypertensions (diencefal syndrome, pheochromocytoma, Conn's syndrome, coarctation of the aorta, renal hypertension, aortic atherosclerosis and thyrotoxicosis). The second stage of the diagnostic system is made for the implementation of this task.