It's a good idea to look up the company's policy on these things before deciding whether to mention it. Local Authorities for example, have a great non-discrimination policy on this and it's actually advantageous to mention it at interview because if you subsequently need time off then they can't give you any grief about it. But not all companies are the same. I would decide on a case by case basis. But if I know somewhere would not want me for that reason, then I'm with Stella, why would I put myself into a hostile environment? The key thing is that whatever you decide, they do not have the right to ask, nor discriminate, but it is often a good idea to be honest without going into details, and always join the union, then you will have protection in the future whilst working.