"It's the first time that we have had an out-and-out cancellation over the issue, and this is a group that has been coming here every three or four years since the 1980s," said Joe D'Alessandro, president and CEO of S.F. Travel, the city's convention bureau.

D'Alessandro declined to name the medical association, saying the bureau still hopes to bring the group back in the future.

As a rule, major conventions book their visits at least five years in advance. So when D'Alessandro and members of the hospitality industry hadn't heard from the doctors about re-upping, they flew to the organization's Chicago headquarters for a face-to-face meeting with its executive board.