We recommend that the Centers for Medicare & Medicaid Services update its Medicare requirements and corresponding educational material to improve providers' understanding of the Medicare Part B billing requirements for co-surgery procedures, including: updating the Medicare Claims Processing Manual, chapter 12, section 40.8, to ensure billing providers understand that two physicians performing procedures as co-surgeons (including bilateral procedures) must append the co-surgery modifier regardless of whether they are in the same specialty or in different specialties, and providing additional education material to providers clarifying that spinal instrumentation procedure codes must be billed with a co-surgery modifier under Medicare Part B when performed as a co-surgery.