When new patients join a prepaid group practice, their utilization of services is usually higher than it will be in a year or so. This "start-up effect" must be considered when planning for group growth. Demand projections are commonly based on data from outside sources and often fail to consider the many critical implications of the start-up effect. More accurate planning can be accomplished by using concrete start-up analysis based on internal information. Administrators who use careful predictions of demand levels rather than guess-work in their planning will provide their organizations with the foundation for a sound system of dynamic growth management.