I’m looking for the answer to this question: let’s say you have no pre-existing conditions when you first take out a health insurance policy. Then a few years later you get cancer. Will most non-Thai insurance companies then classify the cancer as a pre-existing condition when it is time to renew the policy?

If you read the small print you will see that insurance companies, whether Thai or not, can do whatever they want. If the  cancer is declared cured, then it is no longer a pre-existing condition. 

No, that is not a pre-existing condition.

rule 1: never choose a Thai-based insurance Co, even if their Premium is just a fraction of what international companies charge. You get what you pay for, after all....

1 hour ago, siam2007 said:

rule 1: never choose a Thai-based insurance Co, even if their Premium is just a fraction of what international companies charge. You get what you pay for, after all....

It really depends what people want.