If you already have Medicare Part A (Hospital Insurance) and you’re eligible to enroll in Medicare Part B (Medical Insurance) through a Special Enrollment Period (SEP) because you’re covered under a group health plan (GHP) based on current employment, you have options for how to apply. You can apply online or you can mail your completed CMS 40B, Application for Enrollment in Medicare - Part B (Medical Insurance) to your local Social Security office. You’ll also need to send CMS L564 - Request for Employment Information, and a required proof of employment, Group Health Plan (GHP), or Large Group Health Plan (LGHP) coverage with your 40B form. You can also fax your enrollment forms and evidence of employment and health coverage to your local Social Security office. You can find your local Social Security office by clicking “SSA Office Locator” under the “Related Links” section below. Note: If you don’t already have Part A you can apply online at SSA.gov/benefits/medicare. Visit faq.ssa.gov, or call Social Security toll-free at 1-800-772-1213 for more information.