BACKGROUND Tenosynovial giant cell tumor (TSGCT), also known as giant cell tumor of tendon sheath or pigmented villonodular synovitis, is the most common benign tumor of the tendon and synovium. The intra-articular diffuse type can present as a large infiltrative mass involving adjacent soft tissue and sometimes causes secondary destruction of bone, which leads to radiographic and clinical concern for malignancy. The tumor may also be purely extra-articular. METHODS Here, we report the fine needle aspiration cytology findings of 2 cases of diffuse-type TSGCT with large mononuclear cells with eccentric nuclei, finely granular cytoplasm, and a peripheral well-defined cytoplasmic rim of hemosiderin ("ladybird cells"). CONCLUSIONS Although the presence of ladybird cells has been described in tissue sections of TSGCT, their identification in cytological specimens has not been reported to our knowledge. When observed, their presence may aid in differentiating TSGCT from other lesions with multinucleated osteoclast-type giant cells occurring at or near joints.