Nollaig

There are nearly 800 individual episodes of Doctor Who, of which 108 are missing from the BBC archives. These missing episodes were destroyed by the BBC in the sixties and seventies before the value of the material was recognised. Film versions were simply thrown away, and those that were on video were recorded over due to the high cost of video tape at the time. All of the missing episodes are from the first two Doctors, with Troughton's episodes being the hardest hit. Audio versions of all of the missing episodes exist and have been released on CD by the BBC. Two parts of the Troughton story The Invasion were animated by Cosgrove Hall for the DVD release, but it is a costly process and further reconstructions are unlikely at this point. You can find episodes lists and details of the missing ones on Wikipedia.