What is a Master Complaint in a Class Action or MDL?
By Timo Bakker · July 6, 2026 · 5 min read
When many similar lawsuits are filed against the same defendant (multi-district litigation, or MDL), the court often consolidates them under a "master complaint" — a single document that covers all the plaintiffs' common claims. Here is what that means.
Why master complaints exist
Efficiency. Instead of 500 nearly-identical individual complaints, one master complaint sets out the common facts and legal theories. Each individual plaintiff can then reference the master complaint plus their own individual damages.
How they work
- Multi-district litigation (MDL) is created by the Judicial Panel on Multidistrict Litigation.
- Cases from around the country are transferred to one court.
- Lead counsel is appointed to draft a master complaint.
- Individual plaintiffs then file "short-form complaints" referencing the master complaint plus their specific damages.
Difference from a class action
MDLs with master complaints are common in mass torts (opioids, hip replacement failures, hair relaxer cancer cases). Each plaintiff keeps their individual lawsuit and gets individual damages. In contrast, a class action treats everyone as one class member with uniform recovery. See our class action vs mass tort comparison.
Does master complaint mean class action?
Not automatically. Many MDLs (like most mass torts) do not have class certification — they are just consolidated for pretrial efficiency. Some MDLs also have a class action embedded within.