Adult Still's disease (ASD) is a systemic inflammatory disorder of unknown origin. Several reports have suggested a triggering infection in ASD. We describe a case of ASD associated with acute Mycoplasma pneumoniae infection. The close temporal relationship between ASD and acute infection strongly suggests that M. pneumoniae triggered ASD. We suggest that M. pneumoniae should be added to the list of infectious agents that may play a role in its etiology.