every 3 years and an "invitation" is posted by local health board. (That 's what happens in my area)
I heard it's every 5 years in England, but probably depends on health boards policies.
Lil, alba's right, usually 3 to 5 although there is nothing stopping you from booking an appointment if you have signs that you think may not be right, or even if you feel you want to have one just to put your mind at rest. Sometimes the surgery nurse can perform these so you don't even have to see the doctor or you can go to the well women clinic. I personally think every 5 years is too long but that's my personal view. ES
In France women have smear tests every year as there's a 30% risk in any smear test that cancer cells aren't detected, having one every year lowers that risk. However, if you're not carrying the virus which can cause cervical cancer you can get away with every two years, however this means not changing your partner after the test is done.