Purpose <p>Ethical challenges are common in geriatrics, and moral dilemmas and conflicting interests can arise in advance care planning (ACP). Respecting the wishes of frail, acutely ill older patients while acting in their best interests can be challenging. This study was nested within a cluster randomized controlled trial aimed at implementing ACP in acute geriatric hospital units. The aim of this study was to explore clinicians’ experiences of ethical challenges in geriatric units before and during this implementation project.</p> Methods <p>Eight semi-structured interviews—four focus groups and four dyadic interviews—were conducted with a total of twenty-four participants, including implementation teams and other clinicians from the six intervention units. These participants had engaged in ACP with frail, acutely ill older patients and, preferably, their next of kin. The data were analyzed using Braun and Clarke’s reflexive thematic analysis.</p> Results <p>Four themes were developed: (1) navigating prognostic uncertainty while sustaining hope, (2) providing information that enables understanding and participation, (3) managing family disagreements and emotional strain, and (4) preserving dignity towards the end of life. The findings indicate that ethical challenges were often mitigated rather than intensified through ACP conversations.</p> Conclusion <p>Ethical challenges in acute geriatric care arose when patient autonomy was limited by cognitive impairment, unclear preferences, or family disagreement. Earlier preparation of patients and next of kin through ACP could facilitate early identification of potential disagreements and provide a stronger foundation for dialogue in acute situations.</p> Trial registration <p>ClinicalTrials.gov Identifier: NCT05681585. Registered 03.01.23.</p>