The clinical, histopathological, and immunophenotypic characteristics of four cases of malignancy-associated multicentric reticulohistiocytosis (MMR) and one case each of diffuse cutaneous reticulohistiocytosis (DCR) and isolated reticulohistiocytoma (IR), are reviewed. In all four cases of MMR the cutaneous lesions and joint manifestations were judged to be concurrent with the diagnosis of malignancy. Malignancies observed included one case each of pancreatic adenocarcinoma, squamous cell carcinoma of the lung, metastatic melanoma and intraperitoneal grade 4 mucinous adenocarcinoma of uncertain origin. Histologically, all six cases demonstrated the typical changes of a diffuse histiocytic and multinucleated giant cell infiltrate with ground-glass cytoplasm, predominantly in the upper dermis. Immunohistochemical investigation revealed strong cytoplasmic staining with KP-1 (CD68) in all six cases. Prominent membrane staining was noted with leucocyte common antigen (CD45) in four cases (three MMR and one IR), and CD3 in four cases (three MMR and one IR). Weak membrane staining with Leu 22 (CD43) was noted in two MMR cases. UCHL-1 (CD45RO), L26 (CD20), S-100 and BerH2 stains were all uniformly negative. A prominent number of perilesional factor XIIIa-positive dermal dendrocytes were noted in the single case of IR, in contrast with the other five cases. We conclude that MMR, DCR and IR are histopathologically and immunohistochemically similar. The pattern of immunoreactivity observed is consistent with a monocyte-macrophage origin of the infiltrating tumour cells. We emphasize the paraneoplastic association of multicentric reticulohistiocytosis, which we have observed in four of 13 such cases (31%) evaluated at our institution.