We described the first case of hemophagocytosis in adult onset Still's disease (AOSD) in Taiwan. The 24-year-old male was admitted to our hospital for fever of unknown origin. The diagnosis of AOSD was made according to the 1992 criteria, proposed by Yamaguchi. Extensive studies could not identify any infection or other known underlying disorders for reactive hemophagocytosis except for active AOSD. The patient responded well to non-steroidal anti-inflammatory drugs and glucocorticoid. Hemophagocytic syndrome (HPS) often occurred at the onset of AOSD and half of them did not have leukopenia in the literature reviewed. Our case had the same condition. Pathogenetic mechanism and possible association between AOSD and reactive HPS, and the treatment of HPS associated with AOSD are also discussed.