Simple SummaryT cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) acts as an immune checkpoint on exhausted T cells and has been associated with dismal outcomes in various solid tumors. TIM3 is currently being evaluated as an immunotherapeutic target in multiple clinical trials. Our study shows the significant tumor cell expression of TIM-3 in specific subsets of patients with high risk soft tissue sarcomas (HR-STS). We demonstrate an interaction between TIM-3, tumor infiltrating lymphocyte (TIL) counts and PD-1/PD-L1 expression in patients with HR-STS. TIM-3 could qualify as a potential immunotherapeutic target in HR-STS.Abstract(1) Background: The expression of T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), an immune checkpoint receptor on T cells, has been associated with dismal outcomes and advanced tumor stages in various solid tumors. The blockade of TIM-3 is currently under examination in several clinical trials. This study examines TIM-3 expression in high-risk soft tissue sarcomas (HR-STS). (2) Methods: Tumor cell expression of TIM-3 on protein level was analyzed in pre-treatment biopsies of patients with HR-STS. TIM-3 expression was correlated with clinicopathological parameters including tumor-infiltrating lymphocyte (TIL) counts, programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PDL-1) expression in patients with HR-STS. Survival dependent on the expression of TIM-3 was analyzed. (3) Results: TIM-3 expression was observed in 101 (56%) out of 179 pre-treatment biopsies of patients with HR-STS. TIM-3 expression was significantly more often observed in undifferentiated pleomorphic sarcomas (UPS) compared to other histological subtypes (p< 0.001), high TIL counts (p< 0.001), and high PD-1 (p< 0.001) and PD-L1 expression (p< 0.001). TIM-3 expression did not have a prognostic impact on survival in patients with HR-STS. (4) Conclusions: This is the first study to demonstrate a significant tumor cell expression of TIM-3 in specific subsets of patients with HR-STS. TIM-3 qualifies as a potential immunotherapeutic target in HR-STS.