In many health plans, patients must pay a portion of the services they receive. This payment is called “co-insurance” and is usually a small percentage of the service cost after the plan pays benefits. If the plan pays 70 percent of the cost, the patient pays 30 percent of the cost. If the plan pays 90 percent, the patient pays 10 percent, and so forth. Co-insurance is common for PPO products and less common in HMOs.