SUMMARY INTRODUCTION: Cancer patients and their caregivers incur costs not covered by the Sistema Único de Saúde – SUS(Unified Health System) during their treatment, with expenses related to transportation, symptomatic medications, food, loss of working days, and others. OBJECTIVE: To evaluate the costs incurred and not covered for cancer patients and their caregivers during cancer treatment at SUS. METHODS: This is a cross-sectional study of 110 cancer patients undergoing chemotherapy, radiotherapy, and 88 caregivers in the last month prior to their inclusion in the study. We correlated costs with clinical and sociodemographic variables such as gender, race, age, marital status, education, occupation, place of birth, origin, monthly income, family income, housing, comorbidities, types of cancer, and staging. RESULTS: We observed that the average cost for study patients was R$ 747.92, which corresponds to 78.4% of the minimum wage, and the average cost for caregivers was R$ 118.86, which is 12.46% of the minimum wage. Among all variables analyzed, the average overall monthly cost for patients was positively correlated with the occupation (p = 0.021) and origin (p = 0.038) variables. For the other variables, no significant associations were detected. CONCLUSION: The positive correlation found between occupation and origin variables with costs incurred and not covered for patients suggests that the creation of programs that enable the payment of costs not covered by SUS and the decentralization of access to cancer treatment could potentially facilitate patients' adherence to cancer treatment.