This post prompts me to weigh in with two facts about myself. I don't have any faith in the notion that chemicals or head injuries cause PD, but for the sake of more complete statistics, I was exposed in my early teens to an amount of DDT that killed a big, mature housecat living with us, and when I was seven or so my buddy swung a golf club and accidentally hit my head. A week later I was still walking into trees -- and to this day I have a small dent on the left front side of my skull. As we kids growing up in Shaker Heights used to say, put THAT your pipe and smoke it!