A correlative cytologic and histologic study of 40 cases of histologically highly pleomorphic malignant fibrous histiocytoma (MFH) is presented. The fine-needle aspiration biopsy was performed preoperatively, and a diagnosis of malignant soft-tissue tumor could be established in all cases. The cytologic and histologic features corresponded well with each other. The two main cell types were mono- and multinucleated, large polymorphic, often bizarre, histiocyte-like cells and atypical fibroblast-like cells. For a correct diagnosis of pleomorphic MFH, it is important to recognize atypical large polymorphic tumor cells showing signs of phagocytosis: prominent cytoplasmic vacuolization, cell debris or even well-preserved cells within the tumor cell cytoplasm. Phagocytic activity was easily demonstrated in air-dried and May-Grünwald Giemsa-stained material. The differential diagnosis of MFH as opposed to other soft-tissue sarcomas and pleomorphic carcinomas is discussed. Diagn Cytopathol 1986;2:46-54.