For the past three-and-a-half years, Topps Comics has been publishing a monthly comic based on the X-Files series. Although it is not actually written by X-Files creator Chris Carter, it features his name on every cover and initially it sold "like hot cakes", according to Kevin Lyons of Forbidden Planet, a Dublin comic shop. Inevitably the stories coming out now aren't quite as "fresh" as the originals and sales have begun to drop, but it is still pretty popular.

The very first issue drew on the visitation to three Portuguese children early this century by a luminescent lady, generally believed to be a manifestation of Our Lady. The children were given a number of prophecies - including one allegedly relating to the end of the world - now known as the Secrets of Fatima. The comic raises the possibility that the visitation was actually by aliens. Few other comics cover typical X-Files subject matter. One predecessor might be the Twilight Zone comics, which were also based on a television series; the first series of these came out in the mid-1970s, while a second series appeared for a while in the early 1990s. Both sets are now very hard to come by.

The X-Files, comic version, is read by humans of all ages, from about 10 years up. Issue "zero", based on a pilot episode of the TV show, and issue 1 would now be highly collectable, selling for up to £45 - a big increase in the space of a mere three years. The issue of the comic which ties in to the film adaptation sold out completely the day it arrived in the shops this summer - even though it came out before the film itself. (Shrewd fans and collectors bought the comic and resisted the temptation to read it before seeing the movie.) It, too, is now worth a lot of money, though an exact value won't become clear for some months.

The videos of the television series have also been very cleverly marketed. The first box set contained seasons one through three. Seasons one and two have now been deleted, and original copies are like gold dust.