HMO stands for Health Maintenance Organization, a managed care plan where you have the ability to choose your primary care physician (PCP) from a list of network providers. Your PCP is responsible for management of all aspects relating to your health care. If you require care from any network provider other than your PCP, you may need a referral from your PCP to see that provider. Check with your plan to see if your PCP is also the "gatekeeper" for access to other network providers. You must obtain care from a network provider in order to have your claim paid through the HMO. Treatment received outside the network is generally not covered, or covered at a reduced level.