Tasks, requirements, planning and design of the central data bank in a patient information system are demonstrated by the model of the »Medical System Hanover« (MSH).The Terms »Information System«, in particular »Patient Information System« and »Data Bank« are defined. Based on the ultimate goals of MSH, the task set is formulated and a catalogue of the most important basic requirements of a data bank management system is given as typical for application in a hospital environment. Finally, various points of view that are of essential importance for system planning and design, such as selection of data and structurization of files, are discussed.