A: If your spouse’s company has fewer than 20 employees and you enroll in either Part A or Part B, then Medicare is primary and the group-sponsored health insurance will be secondary. If the company has more than 20 employees, the group-sponsored plan is primary and Medicare is secondary. Many people find that the cost of Part B is not worth the secondary coverage. You will need to make sure that the health insurance is considered creditable. Make certain you obtain a letter from your company stating this to avoid paying a late enrollment penalty for Part B later.