A form of health insurance in which its members prepay a premium for the HMO's health services which generally include inpatient and ambulatory care. For the patient, an HMO means reduced out-of-pocket costs (i.e. no deductible), no paperwork (i.e. insurance forms), and only a small copayment for each office visit to cover the paperwork handled by the HMO. An HMO may also be defined as an organization of health care personnel and facilities that provides a comprehensive range of health services to an enrolled population for a fixed sum of money paid in advance for a specified period of time. These health services include a wide variety of medical treatments and consults, inpatient and outpatient hospitalization, home health service, ambulance service, and sometimes dental and pharmacy services. The HMO may be organized as a group model, an individual practice association (IPA), a network model or a staff model.