CPT® Modifier 80 (Assistant Surgeon) is appended to a surgical CPT code when a physician (MD or DO) provides full, continuous assistance throughout the operative procedure. It is intended only for physicians; non‑physician practitioners (PAs, NPs, CNSs) must use HCPCS Modifier AS. Use Modifier 80 when the assisting physician participates for the entire procedure—use Modifier 81 for partial assistance or Modifier 82 when a qualified resident is unavailable in a teaching facility.

Modifier 80 affects payment: under Medicare an assistant surgeon billed with Modifier 80 is reimbursed at approximately 16% of the primary surgeon’s allowable for the same procedure. Whether assistant‑at‑surgery payment is allowed depends on the Medicare Physician Fee Schedule (MPFS) assistant‑at‑surgery indicator (0 = payment allowed only with documented medical necessity; 1 = not payable; 2 = routinely payable; 9 = not applicable). Non‑physician assistants billed with Modifier AS receive about 85% of the assistant‑at‑surgery rate (approximately 13.6% of the primary surgeon’s allowable). Always check the MPFS assistant indicator and payer‑specific policies, and ensure documentation identifies the primary and assistant surgeons, details the assistant’s continuous involvement, and supports medical necessity when required.

Do not append Modifier 80 when a PA, NP, or CNS assists—use Modifier AS instead, and never bill both 80 and AS on the same line. Avoid combining Modifier 80 with co‑surgeon (Modifier 62) or surgical team (Modifier 66) on the same procedure code; these are distinct billing constructs. Because commercial payers may differ from Medicare, verify payer rules before billing.