In this study a review of malignancies classified as histiocytic in the literature is given. The available data suggest that a distinction can be made between three main categories, i.e., follicular dendritic cell (FDC) sarcomas, Langerhans' cell/interdigiting reticulum cell (LC/IRC) sarcomas and histiocytic sarcomas (HS) which are unrelated to accessory cells. With the exception of FDC sarcomas these tumours are high-grade malignancies with an aggressive course and short survival times. The recognition of FDC sarcomas and LC/IRC sarcomas rests upon the identification of accessory cell related antigens (e.g., R4/23, CD1a, S-100) and/or the demonstration of desmosomes or Birbeck granules. The diagnosis of HS which are unrelated to accessory cells is more complex. These tumours are heterogenous with respect to morphology and phenotype and can only be recognized with the use of an extensive panel of antibodies supplemented when possible by analysis of T-cell receptor--or immunoglobulin genes.