Purpose <p>The aim of this study was to assess the extent of financial toxicity in patients with cancer in Slovenia, measured as perceived financial strain and out-of-pocket expenditures.</p> Methods <p>The prospective, cross-sectional study was done at Institute of Oncology Ljubljana from June to October 2023. A newly created individual questionnaire was utilized to obtain data on financial toxicity. Patients completed the questionnaire either on paper or online, with or without the assistance of a researcher. The statistical analysis was based on descriptive and inferential statistics.</p> Results <p>A total of 901 surveys were disseminated, of which 659 were returned, corresponding to a response rate of 73%. Most patients had compulsory health insurance and were diagnosed in the public healthcare system. Following a cancer diagnosis, 178 (27%) patients reported a decline in financial satisfaction (subjective assessment), while 150 (22.7%) patients observed a change in their financial capability (objective assessment). Younger patients (<i>p</i> &lt; 0.001), female patients (<i>p</i> &lt; 0.004), patients with lower net household income (<i>p</i> &lt; 0.001), and patients who were employed before the diagnosis (<i>p</i> &lt; 0.001) were at a greater risk for financial toxicity. Patients with breast cancer and colorectal, endometrial, skin (including melanoma), esophageal, stomach, kidney, bladder cancers, and lymphoma had higher self-reported subjective and objective financial toxicity than patients with prostate, lung, and head and neck cancer.</p> Conclusion <p>This article represents the first comprehensive assessment of financial toxicity among patients with cancer in Slovenia, using perceived financial strain and out-of-pocket expenditures. Most patients reported no significant out-of-pocket costs for the treatment they received. About a quarter of patients with cancer experience financial difficulties.</p>