Although cancer patients may incur a wide range of cancer-related out-of-pocket costs and experience reduced income, the consequences of this financial burden are poorly understood. We investigated: financial adjustments needed to cope with the cancer-related financial burden; financial distress (defined as a reaction to the state of personal finances); and factors that increase risk of financial difficulties. Two sets of semi-structured face-to-face interviews were conducted with 20 patients with breast, lung and prostate cancer and 21 hospital-based oncology social workers (OSWs) in Ireland, which has a mixed public-private healthcare system. Participants were asked about: strategies to cope with the cancer-related financial burden; the impact of the financial burden on the family budget, other aspects of daily life, and wellbeing. OSWs were also asked about patient groups they thought were more likely to experience financial difficulties. The two interview sets were analysed separately using a thematic approach. Financial adjustments included: using savings; borrowing money; relying on family and friends for direct and indirect financial help; and cutting back on household spending. Financial distress was common. Financial difficulties were more likely for patients who were older or younger, working at diagnosis, lacked social support, had dependent children, had low income or had few savings. These issues often interacted with one another. As has been seen in predominantly publically and predominantly privately-funded healthcare settings, a complex mixed public-private healthcare system does not always provide adequate financial protection post-cancer. Our findings highlight the need for a broader set of metrics to measure the financial impact of cancer (and to assess financial protection in health more generally); these should include: out-of-pocket direct medical and non-medical costs; changes in income; financial adjustments (including financial coping strategies and household consumption patterns); and financial distress. In the interim, cancer patients require financial information and advice intermittently post diagnosis.