Could it be that you are unintentionally re-enforcing negative attention getting behavior??? Have you tried IGNORING it? Praise him when you catch him telling the truth. That is what worked with my 14 yr old ADHD son.
Hope this helps.

I have a 20 yr old daughter with ADD and she lies alot too. Even about the smaller things in life. She lies about why she quits her jobs etc. I don't know why and I hope it is not going to repeat itself with my grandson who has ADHD but he sometimes lies as well but he is 5. No answer but you are not alone. Good luck and welcome.

My son who is almost 7 does the same thing from time to time. It was really bad when he was 5. I do what new2day states in her post and it has worked. You have to pick the best battle and leave the rest. Complementing my child when he has told the truth has helped trmendously. He knows now when he is telling the lie and when he is telling the truth. In the begining I do not know that he really new the difference. When he has told a lie that is very serious I wait awhile and then sit down and chat to him about it. I have even made him sit and draw about how the lie he told makes me and others feel. I have drawn a picture to show the truth and how it makes me and others feel. I have posted them next to my daily chart for him. So when he does right or wrong he knows how I and others are feeling. It has gotten way better over time.

Thank you so far to all for the advice. I appreciate it. I have tried all of these suggestions given. The lying seems to get worse as he gets older. He lies about homework, he tells lies about the teacher and even lies about us. He knows the ramifications for lying and the differences between a "white lie" and a lie. He even told his father ( when he went to visit him in the summer) that we allowed him to stay up until 1 in the mornings and we gave him pop tarts to eat for breakfast every morning and he could play outside until 9 pm on school nights.. nothing he says could be further from the truth lol

Hi Jessemum,
I too deal with this problem, and honestly have not found an answer that works. It seems to come in waves....and some of the things my son tells me I swear he thinks are true!
So, I have tried to stick to the rule of..if it is serious I'm a dog with a bone...if it isn't ...I let him know, that I know the truth and shut it down.
Might not be great advice but it gets us by...frustrated in Canada too!!! ( and wet..lol)

Yes, curse the rain in this wonderful country. I, admit, I too have the lying disorder caused by ADHD. I will lie about anything and everything...not necessarily because I WANT to, but because part of me feels guilty...and part of me wants to just get away from it. If I lie about something, then people won't bug me too much about it, until later, but by then they're too busy yelling at me that...all I have to do is...cry. Which doesn't happen in my case...I end up laughing...which only gets me into more trouble...but that's where my nerves come into play. Anyways, lying isn't always done purposefully...sometimes, due to the fact that it's become a habit...it just happens. It's the first thing that comes to mind, the first response out of our mouths. I know this.