Romney, who has acknowledged he is considering a presidential bid (search) but also says he might run for re-election as governor, raised the issue Thursday when asked how he would choose among his political options.
"Any reversal of her good health would almost certainly mean getting out of public office. I wouldn't run for another campaign, almost certainly," Romney said in an interview with The Associated Press.
Ann Romney was diagnosed with the degenerative nerve condition in 1998. She is currently in good health.
In 2002, Romney also cited his wife's condition as a factor in his political future when, fresh from his success leading the Winter Olympics (search) in Salt Lake City, he was considering whether to run for governor in Massachusetts.
While Romney's presidential aspirations have been a source of speculation for months, he acknowledged his interest in the office earlier this week, calling it "a fair characterization" to say he's testing the national waters.
The governor has recently spent time in South Carolina, Michigan and California to address Republicans, casting himself as a lonely Republican voice in a Democratic stronghold and a social conservative on such issues as same-sex marriage and stem cell research.
Romney's term as governor expires in 2006. In December, he pledged to run for re-election, but he has gradually backed away from that commitment and now says he'll make up his mind by the fall.
Romney, a former venture capitalist, said Thursday that another determining factor in his future would be how much he's accomplished as governor and what remains of his agenda to reform state government and bring in new jobs and business.
If he does run again for governor, he would be unlikely to leave part-way through a second term to run for president, he said.
"I would expect that people are going to ask for a commitment to be in all four years," Romney said. "That's what they'd expect, and that's what they'd get."