Background: Financial toxicity (FT) describes objective and subjective burden of costs associated with medical care. Patients with head and neck cancer (HNC) and lung carcinoma are acutely impacted by FT, as these cancers disproportionately occur in populations that are poor, unemployed, and/or of minority backgrounds compared to patients with other cancers. Our group recently published results showing delay in time to treatment initiation (TTI) was associated with poorer survival in HNC patients. Another study reported that FT was associated with worse progression-free survival in non-small cell lung cancer patients. In this study, we sought to investigate the association between FT, TTI and clinical outcomes among HNC and lung carcinoma patients, as well as predictors of FT. Methods: A retrospective analysis of 140 patients diagnosed with either HNC or lung carcinoma between January 2007 and March 2018 with quality-of-life data collected prospectively at the time of radiation oncology treatment was conducted. Participants responded to a question about their experience on ‘financial difficulties’ with a 4-point Likert Scale within the European Organization for the Research and Treatment of Cancer Core Quality of Life Questionnaire (EORTC QLQ-C30) quality of life assessment. FT was low when patients indicated ‘1’ (not at all) or ‘2’ (a little), and high if patients indicated ‘3’ (quite a bit), and ‘4’ (very much). Chi-square test and Student’s t-test were used to compare characteristics of patients with and without FT. The association between FT and TTI and survival outcomes were analyzed using the Kaplan-Meier methods and Cox proportional-hazards regression models. Results: The study sample included 70 patients with HNC (mean [SD] age, 64.3 [12.0]; 62.7% male) and 70 patients with lung carcinoma (mean [SD] age, 69.1 [10.2]; 38.0% male). Over half (N = 80, 55.2%) reported experiencing financial toxicity (64% HNC vs. 45.7% lung carcinoma). Younger age (< 60 years), having Medicaid, and having small-cell lung carcinoma were associated with greater FT (p = 0.049, p = 0.042, p = 0.034, respectively). Patients who reported having poorer health and quality of life also experienced greater FT (p = 0.030, p = 0.016, respectively). HNC patients who experienced greater FT were less likely to experience treatment delay (p = 0.035). After adjusting for age, sex, ethnicity, tumor site, and tumor stage, FT was associated with worse survival outcomes in all patients (HR = 1.52, 95% CI 1.06-2.19). Conclusions: Greater FT was associated with younger age, having Medicaid, and having small-cell lung carcinoma. HNC patients who experienced greater FT were less likely to experience treatment delay, which suggests that delay may not be a causative factor for the worsened survival seen with patients who report FT.