The nodularity and presence of T-cell rosettes surrounding the neoplastic cells has been described as a defining feature of nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL). We have explored the potential diagnostic value of a new marker (NAT105) that recognizes the antigen PD-1 in a series of 152 cases diagnosed as nodular sclerosis Hodgkin lymphoma, mixed cellularity Hodgkin lymphoma, lymphocyte-rich classic Hodgkin lymphoma, NLPHL, and T-cell/histiocyte-rich B-cell lymphoma (T/HRBCL). All the cases were immunostained with a panel of antibodies against CD10, bcl-6, CXCL13, CD57, and PD-1 (NAT-105). The series includes a set of cases diagnosed as NLPHL with diffuse areas, and a group of borderline cases with features between those of NLPHL and T/HRBCL. Results show that PD-1 (NAT-105) is an excellent immunomarker not only of follicular T-cell rosettes in NLPHL, but also of a subset of lymphocyte-rich classic Hodgkin lymphomas. However, it is not a unique and defining feature of NLPHL. The presence of PD-1-positive (NAT-105) T-cell rosettes seems to be an additional useful feature in the differential diagnosis of NLPHL and T/HRBCL, which is normally a controversial and difficult task. The standard T/HRBCL cases lack follicular T-cell rosettes, whereas most of the borderline cases between the 2 entities have follicular T-cell rosettes, thus suggesting a closer relation with NLPHL.