Yes, it is possible to get health insurance even with a preexisting condition. In most cases, there will be a waiting period before the preexisting condition is covered; other health issues that occur during that time and regular check-ups would still be covered.
You can get insurance for preexisting, but you are going to pay the price. Call around to insurance companies for rates, sometimes if they have open enrollment you can get in at a cheaper price.
It is best to disclose it on the application and try to get a policy that will cover it. Sometimes they may reject you, or they may ask you to pay more for your policy. But if you hide it and they find out later it will be denied as pre-existing unless you have pre-existing credit.