Soon after the Office of Inspector General (OIG) reported that three Medicare carriers had overpaid ASC claims over a five-year period for multiple procedures in the same operative session, Nationwide Mutual Insurance Company, Blue Cross and Blue Shield of Kansas and TrailBlazer Health Enterprises decided to recoup the overpayments. The three carriers said they would use the OIG's report and their own records to confirm the number of cases, dollar amounts and providers they overpaid from 1997-2001. Here's how such overpayment can occur and what to do if your facility ever has to refund payments it received in error.