Should I tell my dad with dementia that his brother is dying?

I definately think you should tell him. There are times w/ dementia thet a person is clearer than other times. After all you will later not be wondering if you should have told him. If you have a picture of his brother, maybe it would help to get the message across.

Well, how bad is the dementia? Is this something that you're going to have to repeat a hundred times, or can he remember a little better than that? My mother-in-law also has dementia/alz and her memory is AWOL big time. BUT I do tell her things that I know she would want to know IF she had her marbles still. However, once I tell her life altering things, I do have to repeat them on a regular basis till it becomes 'old information' and she will remember (sometimes) Let's face it, it's a crap shoot as to whether she really remembers it finally, but I feel like I need to watch her back, so I tell her anyway. :)