The first case of primary gamma/delta cutaneous T-cell lymphoma (CTCL) with a fatal outcome is reported. The patient had the clinical and histopathologic features of disseminated pagetoid reticulosis, a rare form of CTCL characterized by a strong epidermotropic lymphoid infiltrate. Extensive immuno-cytochemical studies showed that the neoplastic cells were almost exclusively localized in the epidermis, expressed the gamma/delta variant of the T-cell receptor (CD3+, TCR-delta-1+) and were CD5+, CD7+, CD27+, CD29+, CD43+, CD44+, CD45+, CD45RA+, CD54+, CD69+, but beta F1-, Ti gamma a-, BB3-, A13-, CD2-, CD4-, CD8-, CD11a-, CD49d-, CD25-, CD30-, and HLA-DR-. A comparison of our results with those of the literature, which have not included gamma/delta T-cell receptor analysis, suggests that some reported cases of pagetoid reticulosis may have phenotypes similar to our case. Electron microscopy studies demonstrated that the gamma/delta T lymphocytes were villous, containing dense and multivesicular bodies, and formed close contacts with the surrounding keratinocytes, suggesting that these cells should have a role in the skin-associated lymphoid tissue. The proliferating cells in our case might represent the neoplastic counterpart of the recently reported CD2- subset of normal human peripheral blood gamma/delta T lymphocytes.