When Is Medicare Your Primary Insurance? 
There are many so many scenarios where Medicare exists along with other health plans that it is impossible to give a blanket answer to this question . But there are some very good publications put out by Medicare that spell out each situation where Medicare is and is not your primary insurance . You can find this information by going to medicare.gov . Also , you can call COBC -LRB- Medicare Coordination of Benefits Contractor -RRB- at 1-800-999-1188 . 