Randy - I have some thoughts for you on your issue. I know quite a bit about ADD and how it affects marriages - and the more you know about it the better the two of you will do. Here are some specific thoughts:

Get well educated about ADHD so that you can recognize both the not so subtle symptoms and the subtle ones. This will help you cope. I suggest reading "Delivered from Distraction" by Ned Hallowell for a great overview.

Second, I co-author a blog on the topic of how ADD affects marriages, and it is a good resource for people to help them understand what the patterns are (okay, you can call this self promotion if you want, but actually I write the blog because there is a real need for info on this topic out there, and very little is available.) You can find it by typing adhd and marriage into your search engine - it's called Thoughts on ADHD and Marriage. (they won't let me put a link in here because I'm too new a member!) Take a look at what people are posting and the entries.

Anger is really common in these marriages, but how you deal with it is tricky - is she angry at you? at herself? at the world because she thinks she gets an unfair deal? is she angry because you say she has ADD and she doesn't think so? If you two have been married for 20 years, why is she angry now?

While it is easy to fall into the trap of wanting to "change" your wife's behavior, don't. You can't change her behavior, only she can. What you can do, though, is create an environment in which it is easier for her to decide to manage her ADD symptoms (if she actually has ADD - you don't say if she has been officially diagnosed). That type of environment includes acceptance, loving support, a willingness to talk openly without getting defensive or offensive, and a joint commitment to working on what is at the root of your current issues. Sounds like good advice for any marriage, right? The tricky part is knowing what the ADD part is and what the "gee, we just aren't getting along right now" part is.

Anyway, if you want to write a bit more about the anger - how long, what you think the roots are, what role you play in it, and how you feel about it, then perhaps I can give you a couple more ideas.