My insurance approved my surgery, then denied it afterward. Can they do that?

Short answer

Sometimes, yes — a prior authorization is not the same as a guarantee of payment, and insurers say so in the approval letter itself. But a retroactive denial of an already-authorized service is one of the most appealable things in health insurance, and your prior-auth paperwork is the strongest card anyone can hold in an appeal.

Published August 4, 2026

The sequence is jarring: you did everything right, you waited for approval, the surgery happened, and months later an EOB arrives saying the plan won't pay. Nothing about that is normal from where you're standing. From the insurer's side it usually means the claim was reviewed a second time after the fact, and something in that review contradicted the approval.

Find the authorization first. Before you argue anything, get the approval in your hands: the authorization number, the date it was issued, the codes it covered, and the letter or portal record. If the surgeon's office obtained it, their billing department has it. This is the document the whole appeal turns on, and asking for it later is much harder than asking for it now.

Use the phrase. In writing, this is a "retroactive denial of an authorized service." Naming it that way matters — it tells the reviewer exactly which category of decision you're contesting, rather than leaving them to read your letter as a general complaint about a bill.

The escalation ladder, in order:

Internal appeal. Your plan's own review. Include the authorization number and the approval date, and state plainly that the service was authorized before it was performed.
Peer-to-peer review. Your surgeon speaks directly to the plan's medical reviewer, doctor to doctor. Ask the surgeon's office to request one — many denials reverse here, because the clinical reasoning never made it into the paperwork.
External review. An independent reviewer outside the insurance company. It is free to you, decided by doctors, and the outcome is binding on the plan. This is the step most people never take, and it is the one with real teeth.

If the surgery involved an implant or device: device manufacturers often have their own reimbursement support teams whose entire job is helping patients and surgeons get their device covered. They know that plan's history with that device. Call the manufacturer and ask for reimbursement support.

One fork that changes where you can complain. If the appeal fails and you want a regulator involved, which one depends on your plan type. A fully insured plan is regulated by your state's insurance department. A self-funded employer plan is governed by federal law instead, and the U.S. Department of Labor is the relevant body. One question to HR or your insurer — "is my plan self-funded or fully insured?" — tells you which door to knock on.

FAQ

Doesn't prior authorization mean they have to pay?

No, and the approval letter usually says so — authorization confirms medical necessity, it doesn't guarantee payment. Coverage still depends on eligibility, plan terms, and how the claim was submitted. That doesn't make a retroactive denial correct; it makes it appealable rather than automatically void.

What is external review and why does it matter?

An independent, doctor-led review outside the insurance company. It costs you nothing, and the decision binds the plan — meaning if the reviewer says the plan must pay, it pays. It's the strongest step available to a patient and the most commonly skipped.

Should I pay the bill while I appeal?

Ask, in writing, for the account to be held while the appeal is pending, and get the answer in writing too. Paying doesn't strengthen your appeal, and it removes the pressure that keeps the process moving.

The Guide is general information, not legal or medical advice. Insurance rules vary by plan and state, and details change — check the dates on anything state-specific.