In this master's thesis the contemporary steps of designing information systems on the basis of an information model of the process of in-patient medical treatment are analysed. Since designing and managing of business processes is hard to imagine without the support of information, special attention has been given to CASE systems as the representatives of modern tools for the computer support of information systems development. To approach the designing of information systems in the right manner, it is necessary to be familiar with the theory connected to the models of data and the systems for managing the data bases. Because of all these reasons the thesis states the basic concepts and defintions which were later used in the detailed elaboration and the description of the sub-systems of the process of in-patient medical treatment. After the described problems which occur in designing information systems one approached the development and the implementation of sub-systems of the information model of in-patient medical treatment. In the initial phase of the strategy the existing system was analysed and the main goals of the futur information system were defined. In the phase of analyses of the information system detailed elaboration of in-patient medical treatment in hospitals was carried out, beginning from the moment when the patient checked in at a medical institution, over tests to make the diagnosis and up to the point when the patient is released from hospital. Ready screens of the realised application were used in the analysis to ease the monitoring and understanding of the problem. In the next phase, the conceptual and logical model of the data base of information models of the process of in-patient treatment was designed. In the final phase of implementation a user's application was designed and the possibility was worked out to integrate the developed sub-system of the information model of the process of in-patient medical treatment into an integral business system of the hospital. In the summary a coment of the realized application in respect of new technologies was given.