The cytologic findings of an extranodal NK/T-cell lymphoma (NKTCL) presenting as a large adrenal mass with leptomeningeal involvement diagnosed by CT-guided fine-needle aspiration and cerebrospinal fluid (CSF) cytology are described. The 65-year-old Caucasian patient presented with progressive headache and multiple cranial nerve neuropathies. Magnetic resonance imaging showed leptomeningeal enhancement surrounding the conus medullaris and cauda equine, and a subsequent PET/CT demonstrated a large right adrenal gland mass. Fine-needle aspiration of the adrenal mass showed occasional large pleomorphic cells with prominent nucleoli, moderate amounts of cytoplasm, and rare large cells with sparse cytoplasmic granules admixed with numerous small lymphocytes. Initial flow cytometry from this sample showed no clonal B-cell population. Immunoperoxidase stains performed on the cell block/core specimen showed that the large atypical cells were positive for CD2, CD30, CD43 and CD56, TIA-1, granzyme, and perforin, but for none of the other T-cell markers used (CD3, CD4, CD5, CD8, CD45RO), which stained the abundant background lymphocytes. A CSF specimen showed similar neoplastic cells and flow cytometry showed an NK-cell population with aberrant immunophenotype. The cytologic findings of the neoplastic cells and the extensive panel of immunoperoxidase stains allowed the diagnosis of NKTCL, which was confirmed by the subsequent flow-cytometric immunophenotyping performed on the CSF. This is, to the best of our knowledge, the first case of NKTCL diagnosed by FNA of the adrenal gland and by CSF cytology.