The key litigated issue in this appeal was whether Section 251 of the Patent Act permits the use of reissue proceedings to withdraw a terminal disclaimer from an expired patent if that disclaimer was in effect upon issuance of the patent.

This appeal arose after a patent examiner issued an obviousness-type double patenting rejection against Yamazaki's patent application (Original Application) based on Yamazaki's earlier-issued US Patent No. 4,581,476 (the '476 patent). In response, Yamazaki filed a terminal disclaimer affirmatively disclaiming the statutory term of any patent granted on the Original Application that would extend beyond the expiration date of the '476 patent, December 22, 2003.

After amending each independent claim of the Original Application to make the pending claims patentably distinct from the '476 patent claims, Yamazaki submitted a petition to withdraw the recorded terminal disclosure. Prosecution of the Original Application continued and the application was ultimately issued as US Patent No. 6,180,991 (the '991 patent) on January 30, 2001. Because the terminal disclaimer remained in force when the '991 Patent was issued, it cut the patent's enforceable term. If given the full 17-year term permitted under Section 154(c)(1) of the Patent Act, the patent would have expired on January 30, 2018. However, taking account of the approved terminal disclaimer, the USPTO adopted the December 22, 2003 expiration date of the '476 patent and effectively limited the '991 patent to a term of only 35 months.

On January 16, 2002, Yamazaki filed a reissue application to rescind the terminal disclaimer through reissuance of the '991 patent. The examiner rejected Yamazaki's oath and declaration as defective for failing to recite an error upon which a reissue application could be based. Yamazaki appealed to the USPTO Board of Patent Appeals and Interferences (BPAI) in September 2007. The BPAI concluded that the terminal disclaimer had reset the expiration date of the original '991 patent to that of the '476 patent. It held that the USPTO could not reissue the '991 patent to remove the terminal disclaimer under Section 251 of the Patent Act because the statute:

In its December 6, 2012 decision, the US Court of Appeals for the Federal Circuit affirmed the BPAI's ruling and concluded that when the '991 patent issued with its terminal disclaimer in effect, the disclaimer became part of the patent and defined its term.

The court's analysis hinged on its de novo interpretation of Section 251 of the Patent Act, which allows reissue proceedings for correctable errors for "the unexpired part of the term of the original patent."

The parties agreed that the "term of the original patent" defines the bounds of a reissue proceeding under Section 251. Therefore, the court focused its analysis of the effect of a terminal disclaimer on the term of an original patent, by reviewing Section 253 of the Patent Act, which governs both terminal disclaimers and subject-matter disclaimers. It found two aspects of Section 253 important to this appeal:

The Federal Circuit therefore found that Yamazaki's terminal disclaimer eliminated any term from the original '991 patent beyond December 22, 2003. Because of the patent's truncated term, reissue never existed as a remedy to withdraw the terminal disclaimer.

Patent applicants should note that while the reissue statute is grounded in equity as a means to correct a variety of errors in favor of a patentee, it cannot be used to overcome the effects of an approved terminal disclaimer on an expired patent. When a patent issues subject to a terminal disclaimer, the patentee agrees to reduce the term itself by effectively eliminating the disclaimed portion from the enforceable term of the patent. Once the patent expires, the patentee cannot then rely on a reissue proceeding to obtain a longer term by withdrawing such a terminal disclaimer.