AIMS: The diagnosis of cutaneous γδ T-cell lymphoma (GDTCL) requires the identification of γδ chains of the T-cell receptor (TCR). Our aim in this study was, by using a new monoclonal antibody (mAb) against TCRδ, to evaluate TCRδ expression in formalin-fixed paraffin-embedded (FFPE) skin tissue from TCRγ+ cutaneous T-cell lymphoma (CTCL), and to assess TCRδ expression within a spectrum of other cutaneous lymphoproliferative disorders (CLPDs). METHODS AND RESULTS: Twelve cases (10 patients) with TCRγ+ CTCL and 132 additional CLPD cases (127 patients) were examined, including mycosis fungoides (MF) (n = 60), cutaneous GDTCL (n = 15), subcutaneous panniculitis-like T-cell lymphoma (SPTCL) (n = 11), and CD30+ lymphoproliferative disorder (LPD) (n = 24). Clone H-41 against TCRδ was used on a Leica Bond-3 automated stainer to label FFPE slides. H-41 immunostaining was graded as percentage infiltrate: high (50-100%), moderate (10-49%), and low (0-9%). In TCRγ+ tumours, 12 of 12 (100%) patients showed TCRδ expression comparable to TCRγ expression. No (0%) TCRγ+ cases were negative for TCRδ. In all CLPDs, TCRδ expression was as follows: GDTCL, 16 of 20 cases (14 of 15 patients) high, two moderate, and two low; MF, 0 of 60 cases high, nine moderate, and 51 low; CD30+ LPD, one of 24 cases high, two moderate, and 21 low; and SPTCL, 0 of 11 cases (0 of 9 patients) high, two moderate, and two low. Three MF-like cases and one SPTCL-like case showed high expression; the remainder showed low expression. CONCLUSIONS: mAb H-41 against TCRδ matches TCRγ in immunostaining FFPE tissues from GDTCL, supporting H-41 as a replacement for mAb γ3.20. TCRδ expression in our study suggests that the true occurrence of γδ+ non-GDTCL CTCL/CLPD may be lower than suggested by the recent literature.