To investigate the mode of presentation, cytologic features of the plasmacytoid dendritic cells (pDC), and the expression of CD123 and its significance in Kikuchi's disease.CD123 expression was evaluated by EliVision immunohistochemical staining in formalin-fixed and paraffin-embedded tissues from 30 cases of Kikuchi's disease, 5 cases of T cell lymphoma, 10 cases of reactive lymphoid hyperplasia and 10 cases of chronic tonsillitis.Clusters of CD123 positive PDC were observed in Kikuchi's disease (28 of 30 cases, 93.3%) and the staining intensity was more prominent in the PDC at the periphery of the lesion and around the high endothelial venule-like vessels. CD123 showed three staining patterns: membranous (10 cases, 33.3%), cytoplasmic (10 cases, 33.3%), and membranous and cytoplasmic (8 cases, 26.7%). In the control group, CD123 showed cytoplasmic staining in reactive hyperplasia and chronic tonsillitis. Regarding the staining intensity, 12 of 28 cases (42.9%) were 3+ for CD123, 8 of 28 cases (28.6%) were 2+, and 8 of 28 cases (28.6%) were 1+. In contrast, PDC clusters with 1+ staining intensity were observed in 1 of 10 cases of reactive lymphoid hyperplasia; 2 of 10 chronic tonsillitis diseases; and much less in T cell lymphoma.Large cluster of PDC is detected in both proliferative and necrotizing types of Kikuchi's disease, making this a useful adjunctive diagnostic marker.