42 CFR § 407.30 - Limitations on enrollment.
(a) Initial enrollment periods -
(1) Individual under age 65. An individual who has not attained age 65 may have one or more periods of entitlement to hospital insurance, based on disability. Since each period of disability entitlement entitles the individual to hospital insurance and since entitlement to hospital insurance makes the individual eligible for SMI enrollment, an individual may have an SMI initial enrollment period for each continous period of entitlement to hospital insurance.
(2) Individuals who have attained age 65. An individual who has attained age 65 may not have more than one initial enrollment period on the basis of age. However, if the individual develops ESRD after age 65, he or she may have another initial enrollment period based on meeting the requirements of § 406.13 of this chapter.
(b) Number of enrollments. There is no limitation on the number of enrollments.
(c) Coverage under buy-in agreements. For purposes of paragraph (a) of this section, the continued enrollment of an individual following the end of coverage under a State buy-in agreement in considered an initial enrollment.