Part B of Medicare is known as Supplementary Medical Insurance (SMI). This voluntary insurance, provided under title XVIII of the Social Security Act, pays a substantial part of enrollees' expenses for physicians' services, home health services, hospital outpatient services, and medical and other health services not covered by Medicare's Hospital Insurance (HI - Part A).

Anyone who meets the eligibility requirements becomes entitled to SMI if the individual enrolls during a specified enrollment period.

It is possible to be entitled to SMI without being entitled to monthly benefits or HI, but only for those aged 65 or over.

Under the automatic provision as discussed in HI 00805.035, an individual is deemed to have enrolled in SMI upon becoming entitled to HI.

SMI is financed through premiums paid by enrollees and money appropriated from general revenues. The general revenue contribution is about 3 times greater than the amount of premiums paid by enrollees.

Premiums are deducted from RSDI benefits, RR annuities, or Civil Service annuities, whenever possible. Otherwise, they are paid by direct remittance by or for the enrollee.

“Eligible” and its derivatives refer to the requirements (see HI 00805.005) the individual must meet to be able to enroll during an appropriate enrollment period and thus qualify for SMI.

“Enroll” and its derivatives refer to the process by which an eligible individual establishes entitlement to SMI.

“Entitled” describes an eligible person who has enrolled and is covered under Part B as of a legally- specified month, depending on when the enrollment occurred. SMI benefits are payable for covered services received while entitled.

“Enrollment period” refers to the time established by law during which a valid request for enrollment may be filed.