The Health Services Simulator has been developed to predict the demand for medical care of a population of 500,000 in tesms of initial visits, admission to hospitals, and patient days; tests have been conducted that confirm the accuracy of the predictions. The characteristics of demand for medical care by nine age groups have been estimated by a subjective likelihood technique in terms of outpatient visits over time, inpatient days by level of care, duration, operations, and mortality. Resource utilization is related to the demand that is simulated and can be costed. It is proposed that the Health Services Simulator be operationalized for planning purposes on several geographical areas of varied types such as found in the Experimental Health Services Planning and Delivery Systems. The output from simulation will be predictions of workload and resource utilization, allowing comparison of alternative plans including the effects of altered variables on the system.