Hi Polly,
Great question!
I just wrote an article on that very topic and I'll be posting it here probably next week. But in a nutshell, yes...ADHD is highly genetic- it tends to run in families. In fact, children whose parents have ADHD have a 50% chance of developing the condition. And one in four children with ADHD has at least one relative with the disorder.
Keep an eye out for the article which will be in the SharePost area here on the site.
Terry