Carcinoid tumors of the thymus are vanishingly rare, and the characteristic cytologic findings of this condition have never before been reported in Korea. Recently, we encountered a 58-year-old woman who had been suffering from general weakness and weight loss for several months. Radiological imaging revealed a large anterior mediastinal mass. A fine needle aspiration biopsy (FNAB) of the mass showed predominantly scattered single cells, as well as some loose clusters of small cells with scanty cytoplasm. Some of these small cells exhibited plasmacytoid features, with moderately granular cytoplasm. We also discuss the cytological differential diagnosis between thymic carcinoid and other mediastinal tumors.