Adoptive T cell therapy (ACT) is a safe and effective personalized cancer immunotherapy that can comprise naturally occurring ex vivo expanded cells (e.g., tumor-infiltrating lymphocytes [TIL]) or T cells genetically engineered to confer antigen specificity (T-cell receptor [TCR] or chimeric antigen receptor [CAR] engineered T cells) to mediate cancer rejection. In recent years, some ACTs have produced unprecedented breakthrough responses: TIL therapy has moved from melanoma to solid tumor applications, TCR-engineered cells are developed for hematologic and solid tumors, and CAR-engineered T cells have received Food and Drug Administration (FDA) approval for the treatment of patients with certain B-cell malignancies. Although results are encouraging, to date, only a small percentage of patients with advanced malignancies can benefit from ACT. Besides ACT availability and accessibility, treatment-related toxicities represent a major hurdle in the widespread implementation of this therapeutic modality. The large variety of observed toxicities is caused by the infused cell product or as side effects of accompanying medication and chemotherapy. Toxicities can occur immediately or can be delayed. In order to render those highly promising therapeutic approaches safe enough for a wider pool of patients outside of clinical trials, an international consensus for toxicity management needs to be established.