The discretionary nature of an opposition division's decision whether or not to continue the proceedings pursuant to R. 84(2) EPC has to be distinguished from the much more narrow framework within which the boards of appeal decide on the effect of a withdrawal of an opposition. The effect of a withdrawal on the opposition appeal proceedings depends on whether or not the opponent is the sole appellant.

In G 8/93 (OJ 1994, 887) the Enlarged Board held that if the opponent as sole appellant filed a statement withdrawing his opposition, this could only be regarded as a withdrawal of the appeal which immediately and automatically terminated the appeal proceedings as far as all substantive issues were concerned (G 7/91, G 8/91, OJ 1993, 356 and 346). This was irrespective of the patentee's consent. The proceedings were terminated even if in the board's view the requirements under the EPC for maintaining the patent were not met. The Enlarged Board emphasised the distinction between the power to initiate and continue proceedings and the power to clarify the facts in pending proceedings. According to its case law, in appeal proceedings the former was exclusively the province of the appellant, whereas the latter might be exercised by the board subject to Art. 114 EPC 1973 provided proceedings were pending.

In contrast, according to established case law the withdrawal of an opposition has no direct procedural consequences for the appeal proceedings if the opponent was the respondent and the contested patent was revoked by the contested decision (T 629/90, OJ 1992, 654; followed by numerous other decisions, including T 789/89, OJ 1994, 482, T 194/90 and T 627/92, as well as, more recently, T 46/10, T 727/10, T 2061/11, T 1216/12). In such cases, the board must carry out a substantive examination of the opposition division's decision, and can only set aside this decision and reject the opposition if the grounds for opposition do not prejudice the maintenance of the granted patent. The board's examination can include the examination of evidence submitted by the respondent prior to the withdrawal of the opposition (T 629/90, OJ 1992, 654; see also T 900/03, T 340/05, T 46/10, T 727/10, T 817/12). According to T 46/10, the board can also consider any arguments the respondent (opponent) submitted before the withdrawal.

The opposition appeal proceedings are also continued if both the patent proprietor and the opponent have appealed but the opponent withdraws his opposition in the course of the appeal proceedings. The effect of the withdrawal of the opposition is that the appeal is regarded as withdrawn and the opponent ceases to be a party to the appeal proceedings as regards the substantive issues (T 922/01, T 1346/10).