All good things must come to an end. Today Marvel has announced that in October, we will se the end of an era. Uncanny X-Men will conclude with issue #544.
Starting back in 1963, the series originally just had the title X-Men. It was in 1980, half way through the Days of Future Past storyline where the series changed to Uncanny X-Men with issue #142.
The first run of the series was actually canceled in 1970 due to low sales but rather than completely end, previous issues were reprinted. This lasted until 1975 when Chris Claremont wrote Giant-Size X-Men which introduced the new team (with characters such as Wolverine, Storm, Nightcrawler, etc) and continued in X-Men #94.
WIth the upcoming SCHISM story, there will be a divide in the X-Men and one of the results will be the end of this series. Said to be years in the making, when the dust settles, the state of mutantkind will be irreparably changed forever.
It's unfortunate that the original X-Men series is ending. Uncanny X-Men #544 is on sale this October. It will be written by Kieron Gillen with pencils and cover by Greg Land.