Relitigation of Patent Claims

In a patent case, under collateral estoppel, once a court has ruled upon an issue of fact or law, that ruling may preclude relitigation of the same issue or fact in a different suit involving the same parties. Once a patent has been declared invalid, a collateral estoppel barrier is created against further litigation involving the same patent, unless the plaintiff can demonstrate that he or she did not have a full and fair chance to litigate the validity of the patent in the earlier case. Similarly, defendants may be estopped from contesting issues of infringement and patent validity.

The collateral estoppel bar also applies where a reissue examination is sought of a patent when the patent has been held invalid or unenforceable for fraud or violation of duty of disclosure. Ordinarily, collateral estoppel must be raised as an affirmative defense by the party seeking to use it, or else it is waived.


Collateral estoppel requires the following:



  • the issue at stake is identical to the one involved in the prior proceeding;

  • the issue was actually litigated in the prior proceeding;

  • the determination of the issue in the prior litigation must have been a critical and necessary part of the judgment in the first action; and

  • the party against whom collateral estoppel is asserted must have had a full and fair opportunity to litigate the issue in the prior proceeding.

The collateral estoppel bar is inapplicable when the claimant did not have a full and fair opportunity to litigate the issue decided by the other court. Thus, a claimant can file a federal suit to challenge the adequacy of state procedures. The preclusive effect of a state court judgment in a federal proceeding is governed by state law.

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