The process by which a health insurance company determines whether medical bills should be paid for by the health insurance company itself or by another insurer or third party. For example, claims are frequently subject to subrogation when medical care is rendered as the result of an automobile accident. In most cases the automobile insurer is considered the primary payer. When a health insurance company has determined through the subrogation process that the automobile insurer will no longer pay on medical claims, then the health insurance company will typically become the primary payer.