We report two cases of pneumonia caused by Legionella cincinnatiensis, a species previously identified as a pathogen in only one other instance. Both infections occurred in renal transplant recipients who were receiving only moderate doses of immunosuppressive drugs several years after transplantation; both patients had no recent episodes of rejection. Their clinical courses varied from mild symptoms to multisystem organ failure and death. Species identification by direct fluorescent antibody testing was misleading; initial results revealed infection due to Legionella longbeachae for one patient and infection due to Legionella dumoffii for the other patient. Slide agglutination testing eventually identified both isolates as L. cincinnatiensis. Infection with Legionella species, including L. cincinnatiensis, should be considered not only in the first months after transplantation but also later in the posttransplantation period as either a nosocomial or community-acquired infection. © 1994 by The University of Chicago.