AIMS: This study aimed to investigate how hospitals navigate financial coverage of healthcare for undocumented migrants, given the present laws and regulations in Norway. METHODS: This qualitative study used an explorative approach. We collected and studied hospital guidelines for registering and invoicing foreign patients, and interviewed hospital staff from two university hospitals, and undocumented migrants at one non-governmental clinic in Oslo. The first author collected 14 documents and conducted 14 semi-structured, in-depth interviews. The project team used a thematic-analysis-inspired approach to identify patterns of shared meaning in the guidelines and interviews. RESULTS: We found that the hospital guidelines did not account for undocumented migrants. The staff had to navigate between the guidelines and practical implications of undocumented migrant patients not having a resident permit and thus lacking a Norwegian identity number, bank card, or address. We found discrepancies between different staff's expected roles in the registration of patients and in the assessment of patients' ability to pay. The guidelines presumed an active patient and required documentation, which undocumented migrants had difficulty meeting. CONCLUSIONS: The underlying assumption of patients being documented in routines led to a process of othering of undocumented patients and thereby reproducing their marginalised position in the health system, hence depriving them of the right to 'health care that is absolutely necessary and cannot wait'. We recommend that hospitals increase staff's knowledge and capacity to ensure undocumented migrants' right to healthcare.