CPT modifier -78 indicates an unplanned, related return to the operating or procedure room by the same provider during the global postoperative period. It is appended when treatment for a complication or related issue requires re-entry to a formal OR/procedure room and does not restart the original global period. Because preoperative and postoperative services were included in payment for the initial surgery, modifier -78 signals that only the intraoperative portion of the subsequent procedure should be reimbursed; payment is typically reduced compared with the full procedure fee. The modifier is not appropriate for unrelated procedures (use modifier -79) or when the additional treatment is performed outside an operating/procedure room, such as in an office or bedside. Billing should still submit the full usual charge; payers (including CMS) adjust payment to reflect that only intraoperative work is payable under modifier -78.