Purchase travel insurance when you book your trip (we like AIG Travel Guard). Most travel insurance companies WILL recognize pre-existing conditions like MS, but only if you purchase the insurance within 10-15 days of putting down a deposit on the trip. If you miss that window, any MS event will void out your travel insurance and you are on your own. Now if you meant to buy travel insurance and spaced it (I can be such a dolt!), there are plans from Travel Insured International (
www.travelinsured.com) that you can purchase up 30 days after your initial deposit. Remember, "initial deposit" includes any funds to the trip down to the penny. And a word of warning: if you buy your insurance from the same company you are traveling with and they go belly up, you are SOL. So I always recommend buying your insurance from a third party and NOT through your travel agent/company or cruise ship.
Having been all over the world with MS, here are all of my travel tips....
http://www.activemsers.org/tipstrick...ingwithms.html