Dissociate and disassociate have the exact same meaning—namely, to remove from association or to cease associating. Unlike dissemble and disassemble (just one similar word pair), dissociate and disassociate have not undergone differentiation.
Usage guides have traditionally recommended dissociate over disassociate. There is good reason for this, as dissociate is older by far. But the fact that disassociate is so common—and increasingly so—suggests that we’re probably going to have to accept it. For now, though, dissociate is still more common. As of July 2010, dissociate appears in 1,800,000 Google results, while disassociate appears in 545,000.
Examples
As for major journalistic publications, The New York Times appears to use both dissociate and disassociate, but disassociate appears more often:
That would be this Friday, during the third round of the $8.5-million match-play tournament sponsored by the first company to disassociate itself from Woods . . . [NYT]
Although the technology of the cars is not the highest in the world and is not the race’s main attraction, it is impossible to dissociate the technology from the human challenge. [NYT]
The Wall Street Journal uses disassociate:
Having played so prominent a role in last October’s talks with Iran, the U.S. can’t easily disassociate itself from something broadly in line with that framework. [WSJ]
In the U.K., The Telegraph uses both words on a more or less equal basis:
The Tory brand . . . was so toxic that ordinary people wanted to disassociate themselves even from policies which they would otherwise approve of . . . [Telegraph]
After a difficult first year, the president is trying to dissociate himself from complex bills . . . [Telegraph]
The Guardian prefers dissociate:
Careful to dissociate himself from backward-looking nostalgia, he argued for an open and renewable sense of national identity . . . [Guardian]
