Abstract It has been suggested that plasmacytoid monocytes (PMOs) play an essential role in T-cell-dependent immune response. Indeed, numerous PMOs are found in close topographical association with epithelioid cell granulomas in hypersensitivity-type granulomas, such as tuberculosis and sarcoidosis. The key pathologic process in cat scratch disease (CSD) usually involves a B-cell-associated granulomatous reaction. Histologically, CSD appears to exhibit a histopathologic diversity, including suppurative lesions without epithelioid cell granulomas (early lesion), in which the microabscesses were surrounded by monocytoid B-cells (MBCs), suppurative granulomas containing MBCs (intermediate lesion), and suppurative granulomas without MBCs (late lesion). However, the presence or absence of PMO in CSD has not been studied previously. We examined 14 cases of CSD. In early lesions, numerous clusters of PMO were detected in the MBCs. In intermediate lesions, both MBCs and PMOs were found to be decreased in number, while late lesions contained no or only a few MBCs and PMOs. Overall, these findings suggest that PMOs may play a role in MBC-associated granulomatous response and in hypersensitivity granulomatous response. Moreover, the association with MBCs and PMOs indicates a functional relationship of MBCs with PMOs in the formation of suppurative lesions in CSD.