My vet likes to do it at 4/5 months, but sadly the receptionist told me 6, so Shadow wasn't done until 6months (it was at the post-op check i found out my vets views) - and CP are recommending either 3 or 4 months now. I do know of vets and rescues in my area that do them at 8-10 weeks old, and I think it should be done more often, there could never be any accidental pregnancies then. If some vets can do it at 10 weeks, then there is no excuse for waiting till 6 to find their 'bits'.