You don’t have to, but there are good reasons why you should. In fact, the VA strongly recommends that all veterans who have VA health care also enroll in Medicare as soon as they become eligible.
 
VA health coverage isn’t set in stone and isn’t the same for everyone. The VA assigns enrolees to different priority levels according to various factors, such as income and whether they have any medical condition that derives from their military service.
 
Having both Medicare and VA benefits widens your coverage. If you need to go to a non-VA hospital or doctor, you’re automatically covered under Medicare Part A (hospitalization) and Part B (doctors and outpatient services)—whereas with VA coverage alone, you may end up having to pay the full cost yourself.​