Section 417.420 - Basic rules on enrollment and entitlement(a)Enrollment. Eligible individuals who are entitled to benefits under both Part A and Part B of Medicare or only Part B may elect to receive those benefits through an HMO or CMP that has in effect a contract with CMS under subpart L of this part.(b)Entitlement. If a Medicare beneficiary enrolls with an HMO or CMP, CMS pays the HMO or CMP on his or her behalf for the services to which he or she is entitled.(c)Beneficiary liability.(1) The HMO or CMP may require payment, in the form of premiums or otherwise, from individuals for services not covered under Medicare, as well as deductible and coinsurance amounts attributable to Medicare covered services.(2) As described in § 417.448 , Medicare enrollees of risk HMOs or CMPs are liable for services that they obtain from sources other than the HMO or CMP, unless the services are- (i) Emergency or urgently needed; or(ii) Determined, on appeal under subpart Q of this part, to be services that should have been furnished by the HMO or CMP.50 FR 1346, Jan. 10, 1985, as amended at 58 FR 38078, July 15, 1993; 60 FR 45677, Sept. 1, 1995; 80 FR 7958, Feb. 12, 2015