Vibrating as I brake

My 2000 Sport has 150,000 miles on it, runs great. Noticed a bad vibration when I brake. I can feel it in the wheel but it sort of seems to be coming from the rear end. Is it just bad rotors or is it a bigger problem?

Thanks

It's likely the brake rotors are warped - not surprising at 150k. Is the vibration worse when you slow from say, 65 mph than when slowing from 45? If so it's time to either have them turned (machined to remove some material and get the faces flat again) or replaced.