The 30-month coordination period, for people with End-Stage Renal Disease (ESRD), is the period when a group health plan (GHP) pays first and Medicare pays second for health care costs. The coordination period begins when your eligibility for ESRD Medicare begins, even if you haven’t enrolled for ESRD Medicare yet. Even though your GHP pays primary during this period, you may want to enroll in ESRD Medicare, as it may cover remaining costs.