Background: Chimeric Antigen Receptor (CAR) T cell therapy provides promising outcomes in relapsed/refractory B Acute Lymphoblastic Leukemia (ALL) yet still carries high toxicities rates and relatively poor long-term survival. Efficacy has yet to be demonstrated in other diagnoses while toxicity and risk profiles remain formidable. To date, treatment-related symptom burden is gleaned from clinical trial toxicity reports; the patient perspective remains understudied. Methods: English or Spanish-speaking patients (ages 8-25 years) undergoing CAR T cell therapy for any malignancy and their primary caregiver were recruited from Seattle Children’s Hospital (SCH), St. Jude Children’s Research Hospital (SJCRH), and the Pediatric Oncology Branch of the National Cancer Institute (NCI). Both patient and caregiver completed semi-structured dyadic interviews 3-months post-treatment. We used directed content analysis for codebook development and thematic network analysis for inductive qualitative analysis. Results: Twenty families completed interviews (13 patients, 15 parents). Patients were a median age 16.5 years, predominantly female (65%), white (75%), and diagnosed with ALL (75%). Global themes included “A clear decision,” “Coping with symptoms,” and “Unforeseen psychosocial challenges.” When families were asked to describe the “most challenging part of treatment,” most described “the unknown.” Most reported “the symptoms really weren’t that bad,” even among patients hospitalized for severe toxicity events. Fatigue, pain, and nausea were the most prevalent symptoms. Importantly, only one family would have chosen a different therapy, if given another opportunity. Conclusions: Although physical symptoms were largely tolerable, recognizing supportive care opportunities remains imperative, particularly psychosocial concerns.