Therapies targeting the programmed cell death 1 (PD-1) or its ligand (PD-L1) promote antitumor T-cell activity, leading to unprecedented long-lasting tumor responses in some advanced cancers. Because of radiotherapy and chemotherapy resistance, no effective treatments have been defined for advanced chondrosarcomas. We here report an immunohistochemical analysis of PD-L1 expression in a large series of conventional, mesenchymal, clear cell and dedifferentiated chondrosarcomas using tissue microarrays. In the PD-L1-positive tumors, we analyzed the immune microenvironment (T-cell and macrophage infiltration as well as HLA class I expression) using whole sections. PD-L1 expression was absent in conventional (n = 119), mesenchymal (n = 19) and clear cell (n = 20) chondrosarcomas. Forty-one percent (9 of the 22) of dedifferentiated chondrosarcomas displayed PD-L1 positivity. These results were confirmed in an independent cohort using whole tissue sections of dedifferentiated chondrosarcomas in which PD-L1 expression was detected in 52% (11 of the 21) of cases. PD-L1 expression was exclusively found in the dedifferentiated component and expression positively correlated with other immune parameters such as high number of tumor-infiltrating lymphocytes (P = 0.014) and positive HLA class I expression (P = 0.024) but not with patient overall survival (P = 0. Chondrosarcomas constitute a malignant group of cartilaginous matrix-producing neoplasms, with diverse morphological features and clinical behavior. 1 Conventional chondrosarcoma is the second most common primary bone malignancy after osteosarcoma and can be categorized according to their location into central (85%) and peripheral chondrosarcomas (15%). Their histology is similar, with atypical chondrocytes and abundant extracellular matrix, but they differ at the genetic level. Notably, mutations in isocitrate dehydrogenase (IDH) 1 and 2 are found in approximately half of conventional central chondrosarcomas while mutations in genes encoding exostosin (EXT) 1 and 2 characterize peripheral chondrosarcomas. 2,3 Histological grade is strongly correlated with clinical prognosis with a 10-year survival rate of 83% for atypical cartilaginous tumor/grade I but only 29% for grade III. In addition to conventional chondrosarcoma, several rare subtypes of chondrosarcoma are discerned (dedifferentiated, mesenchymal and clear cell), together constituting 10-15% of all chondrosarcomas. Clear cell chondrosarcoma is a low-grade malignant tumor with a 10-year survival rate reported around 90% while dedifferentiated and mesenchymal chondrosarcoma are both highly malignant, with frequent occurrence of distant metastases and o30% survival at 5 and 10 years, respectively. 4