PURPOSE In patients with metastatic breast cancer (MBC), low health insurance literacy may be associated with adverse material conditions, psychological response, and coping behaviors because of financial hardship (FH). This study explored the relationship between health insurance literacy and FH in women with MBC. METHODS This cross-sectional study used data collected from 84 women receiving MBC treatment at 2 southeastern cancer centers. Low health insurance literacy was defined as not knowing premium or deductible costs. FH was defined by lifestyle changes as a result of medical expenses, financial toxicity, and medical care modifications attributable to cost. Mean differences were calculated using Cramer’s V. Associations between health insurance literacy and FH were estimated with adjusted linear models. RESULTS Half of the surveyed patients had low health insurance literacy, 26% were underinsured, 45% had private insurance, 39% had Medicare, and 15% had Medicaid. Patients with low health insurance literacy more often reported borrowing money (19% v 4%; V = 0.35); an inability to pay for basic necessities like food, heat, or rent (10% v 4%; V = 0.18); and skipping a procedure (8% v 1%; V = 0.21), medical test (7% v 0%; V = 0.30), or treatment (4% v 0%; V = 0.20) compared with patients with high health insurance literacy. Median Comprehensive Score for Financial Toxicity was 23 (interquartile range, 17-29). In adjusted models, health insurance literacy was not associated with financial toxicity. CONCLUSION Low health insurance literacy was common in women receiving MBC treatment. Additional research to increase health insurance literacy could lessen undesirable material FH and unnecessary behavioral FH associated with cancer-related care.