Background: Patients with cancer experience financial toxicity from the costs of treatment, as well as material and psychologic stress related to this burden. A synthesized understanding of predictors and outcomes of the financial burdens associated with cancer care is needed to underpin strategic responses in oncology care. This study systematically reviewed risk factors and outcomes associated with financial burdens related to cancer treatment. Methods: MEDLINE, Embase, PubMed, PsychINFO, and the Cochrane Library were searched from study inception through June 2018, and reference lists were scanned from studies of patient-level predictors and outcomes of financial burdens in US patients with cancer (aged ≥18 years). Two reviewers conducted screening, abstraction, and quality assessment. Variables associated with financial burdens were synthesized. When possible, pooled estimates of associations were calculated using random-effects models. Results: A total of 74 observational studies of financial burdens in 598,751 patients with cancer were identified, among which 49% of patients reported material or psychologic financial burdens (95% CI, 41%–56%). Socioeconomic predictors of worse financial burdens with treatment were lack of health insurance, lower income, unemployment, and younger age at cancer diagnosis. Compared with patients with health insurance, those who were uninsured demonstrated twice the odds of financial burdens (pooled odds ratio [OR], 2.09; 95% CI, 1.33–3.30). Financial burdens were most severe early in cancer treatment, did not differ by disease site, and were associated with worse health-related quality of life (HRQoL) and nearly twice the odds of cancer medication nonadherence (pooled OR, 1.70; 95% CI, 1.13–2.56). Only a single study demonstrated an association with increased mortality. Studies assessing the comparative effectiveness of interventions to mitigate financial burdens in patients with cancer were lacking. Conclusions: Evidence showed that financial burdens are common, disproportionately impacting younger and socioeconomically disadvantaged patients with cancer, across disease sites, and are associated with worse treatment adherence and HRQoL. Available evidence helped identify vulnerable patients needing oncology provider engagement and response, but evidence is critically needed on the effectiveness of interventions designed to mitigate financial burden and impact.