Multiple myeloma (MM) with central nervous system (CNS) infiltration is uncommon and the diagnosis is more complicated than that of MM. Here we report two cases of CNS MM that was diagnosed by cerebrospinal fluid cytology examination. Cerebrospinal fluid cytology examination can help to detect malignant cells and immunocytochemistry stain is of great value in identifying an unknown tumor. Diagn. Cytopathol. 2017;45:66–68.