How long can a series still keep its fans? Is there a general rule to that? Do they know when to stop? I have thought long about that. One of my favorite show ER is currently showing its 12th season. If someone had told me at its beginning that I would still be watching 12 years later, I probably would have laughed and doubted that any show could be so long on air. You have to admit that usually medical shows never lasted that long. I'm less surprised by the everlasting and always great Law and Order. It survived the constant change of main characters pretty well and watching it now is still a pleasure. Crime series have this capacity to easily find new stories to tell. Just open a newspaper in any country you probably have at least one or two stories that be easily told. Most of the time the personal life of the main characters are little addressed (probably with the exception of NYPD Blue) and start to wonder if this is not the way to success and longevity. The less you know, the more you can decide for yourself what their private lifes look like. Many people tend to be shippers, seeing chemistry between two actors and wanting a certain amount of sexual tension even if there is nothing there and TPTB don't want to go this way. So not addressing is maybe giving to everyone what they want. Most of the time I used to like series that were not front-runners (ER and L&O being the exception). The Pretender didn't last beyond its 4th year, same thing for Farscape and many others (I will not even start with the ones, which didn't even make their first year! How could people not like Profit, this series was simply great and so very different?!?). Then started the reign of CSI and suddenly I discovered that I was not alone out there with a morbid taste for criminal series. You get here an interesting mix of easy-to-understand criminal science and an appealing cast. Will it last? I sure hope so. But can the show survive the departure of leading actors? Well I would say, it depends. I'm honestly not sure that CSI Miami would last long without D. Caruso, he is the leading force and the others are definitely in the background. As far as the original CSI is concerned I'm more optimistic. William Petersen is great, but the show is better balanced and even Grissom-light episodes were hits. But let's wait, it's still early. Losing leading actors is probably one of the main reasons why series stop. Would you want to see Buffy without Buffy? Well clearly not... Being a TV addict, one thing always stroke me as vital in a series survival : how did the writers deal with the 3rd season? It seems to have been most of the time the critical one. If the show didn't perform well that year, it was usually given an additional year to make it interesting for syndication (you usually to have at least 90 episodes) but that was it. I saw it with The Pretender, ST Enterprise and many others. So what is so dangerous about the 3rd year? Well the first season is usually used to introduce the characters and set your story. If the concept is interesting and the series well cast, it shouldn't be an issue to get a second year (sure there are exception, sometimes the public is simply not ready for some stories). Season 2 is when you need to develop your concept and get in rhythm. It's still new and appealing. With season 3, problems start. Say good-bye to novelty and hallo to the fierce competition of newly started shows! This is when TPTB have to keep their public interested. It is usually when most writers and producers make majors mistakes to attract more viewers. They have become greedy and seem unable to prevent unwanted story twists which don't attract a new audience and tire or disgust the faithful fans. There is also another phenomenon : fans expecting too much from a show. How can that happen? Some series are rich with mysteries (excellent example being Lost) and fans spend many time trying to figure out what is going to happen next. I have hit the net and I must admit some theories are really very interesting. I just hope that the actual story will be as good. Let's sit back and wait and see. Another risk comes from complicated story-lines. Don't lose your audience on the way! That's what Babylon 5 did wrong. It was one great series, but hell if you missed one episode you were almost doomed! I must admit that a mix of this and of too high expectations is what drove me away from Alias. I used to love the show, but the constant twists in this series made me nauseous. It was worse than being in a roller-coaster. There is only so much one can take. Season 3 did it to me. I gave up... Ratings are the almighty hand that finally nails the coffin. Even with decreasing numbers ER is still present on air. The audience is still good and there is another factor: foreign networks which are very eager to air the show in their countries! Can then a show with limited ratings but high commercial value abroad survive longer? Well only on a limited basis. Babylon 5 was supposed to be axed in its 3rd season. German and Dutch producing companies came to its rescue and made it possible for it to go to the fifth year. But I'm afraid you won't find many other examples of something like that.