In a method for defining the time and scope of maintenance operations for a system having a plurality of maintenance items, each of which should be carried out within an assigned tolerance range, a minimum maintenance interval between successive maintenance operations is predefined. The timing of a maintenance operation is predictively fixed at at least that tolerance range end point which is the first of the tolerance range end points of maintenance items relating to maintenance times to follow the time of a preceding maintenance operation while complying with the minimum maintenance interval. At least those maintenance operations whose tolerance range end points occur before the predicted subsequent maintenance time are defined as the scope of the imminent maintenance operation.