Creator Vince Gilligan recently told The New York Times that the 5th season of Breaking Bad (the show is currently in it's 4th season), will be it's last.

"This was never intended to be an open-ended show," he said. "As creators of the show, we have to see it through to the end, to finish what we started."
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Actor Bryan Cranston added:

"We're able to manipulate time, so that even though we're four years into the show, we're only a year into the story," Mr. Cranston explained. "The conceit was that Walter White was given a diagnosis of two years to live. We're going to hold to that and, by the end of the series, I can't imagine him not dying. Although it may not be from lung cancer."