- In this paper we present a general model and solution methodology for planning resource requirements (i.e., capacity) in health care organizations. To illustrate the general model, we consider a specific application: an actual health maintenance organization (HMO) from which we collected real data. The HMO capacity planning problem involves determining the number of examining rooms required and the size of the medical staff necessary. Capacity must be sufficient to handle the expected number of patients without causing excessive waiting times. To determine resource requirements, we develop an optimization/queueing network model that minimizes capacity costs while controlling customer service by enforcing a set of performance constraints, such as setting an upper limit on the expected time a patient spends in the system. The queueing network model allows us to capture the stochastic behavior of health care systems and to measure customer service levels within the optimization framework.