Well as someone who is a former smoker and loved every puff I ever took this is a topic that I felt I had to address in my personal life. Yes it does seem as if smoking can possibly increase the chance of being diagnosed as well as the progression of multiple sclerosis. I was not able to reconcile taking a chance with something that might increase the damage this disease will do to me so I quit for the last time over 6 years ago.

In addition to what appears to be credible studies another reason I took such heed to the mumblings of the extra dangers of smoking for people with ms was a post I read on a ms message board. This member described going to a large MS convention and not being able to get close enough to use to the ash tray because of all the people in wheel chairs gathered around them. That image haunts me on several levels.

Google scholar resulted in over 46,000 hits for: smoking and multiple sclerosis
Note those parameters also included marijuana articles.

"These results support the hypothesis that cigarette smoking is associated with an increased risk of multiple sclerosis, and suggest that smoking may be a risk factor for transforming a relapsing–remitting clinical course into a secondary progressive course." from:
http://brain.oxfordjournals.org/content/128/6/1461.full