A recent trademark decision at the Federal Circuit Court of Appeals (CAFC) denied registration to an application that was filed in 2001. See TTABlog® summary here. The application, appeal to the TTAB, and appeal to the CAFC took more than 15 years!
That got me wondering how many trademark applications are still pending with filing dates from last century – I mean, last millennium? The answer is 54, I think. Based on the following TESS search of the USPTO database: (19??????)[FD] and (live)[LD] and (0)[rn] not (89??????)[sn] there are 54 results. See below. Some of these are in litigation/disputes (for example, an application for HANAVA CLUB is the subject of a well-known longstanding disputes, as is one for the WASHINGTON REDSKINS) . Some are held up due to possible conflicts with other trademarks applications in disputes. It is safe to say, that since they are pending more than 15 years, they all have interesting and complex histories.
Based on the serial numbers assigned to the applications, it appears that the oldest pending application in the USPTO records was filed on Mark 24, 1988, for the VAVAIO PANCALDI logo below. The application was suspended in March of 1989 due to a dispute filed with the owner of a registration for PANCALDI & Design. That dispute appears to have been ongoing ever since. See full details from TSDR here and TTABvue here.
Tip: experienced counsel, trademark docketing software, and knowledge of the USPTO trademark application process are very valuable when filing any trademark application — because you never know how long that application may last!