Occasionally, the world champion of a particular weight division is temporarily unable to defend his championship because of medical, legal, or other reasons that are beyond the champion's control. When this case occurs, two highly ranked contenders will fight for the interim championship of the same weight division—leading to two champions existing in the same weight division simultaneously. Once the world champion is able to return, he must fight against the interim champion. The winner of this bout reunifies the weight division as sole world champion. If the world champion cannot return or moves to a different weight division, the interim champion becomes the world champion.
Sanctioning bodies, however, sometimes abuse the interim championship system. One example was in the WBC's flyweight division in 2005–2006. Pongsaklek Wonjongkam had defended his world title 11 consecutive times. Number-one contender Jorge Arce won an interim championship bout instead of receiving a title shot against Wonjongkam, who continued to defend his world title. Arce defended his interim championship four times before he vacated it in order to move up to super flyweight. Wonjongkam eventually set the flyweight division record for consecutive title defenses, without ever fighting against interim champion Arce.