Health Maintenance Organizations (HMOs) usually have copayments instead of deductibles, co-insurance and no lifetime limit on coverage. You must receive all of your medical care from network providers, except in emergencies. Once you enroll in an HMO, you select a primary care physician who will be responsible for coordinating all of your care. Whenever you require treatment (other than emergencies), you must first see your primary care doctor who will refer you to a specialist, if necessary. You may not receive coverage without the referral, and the specialist must be a network provider. Hospital admission requires pre-certification from your plan, arranged by your physician or the hospital. It it's an emergency, you or a family member, your doctor, or your hospital must contact your plan usually within 48 hours of admission to obtain written confirmation of coverage for the hospital stay.