How to convince him

My husband was diagnosed with ADHD when he was a child.  I believe he was put on medication, but I'm not really sure because he won't talk about it at all.  Now he believes he's grown out of it and it doesn't affect him at all.  I can see that it's not true, but he can't.  How can you possibly convince someone to seek diagnosis and treatment if they don't think they have a problem?