Background <p>Advance care planning and respect for patient autonomy are central concerns in contemporary medical ethics, particularly for patients whose decision-making capacity may be impaired. This study aimed to examine and identify ethical challenges in judicial judgments in Japan relating to these patients.</p> Methods <p>We conducted a retrospective observational study of Japanese civil court judgments using Westlaw Japan. We systematically identified judgments addressing physicians’ duties of explanation or informed consent for patients with impaired decision-making capacity. Cases were limited to judgments rendered after May 2007, following publication of the national Guidelines on the Decision-Making Process for Medical Care and Care at the End of Life in Japan. We evaluated five items: (1) substantive consideration of patients’ wishes and values; (2) individualized assessment of decision-making capacity and underlying conditions; (3) whether family members’ wishes were treated merely as surrogate consent; (4) whether a repeated, dialogical decision-making process involving family members and healthcare or care teams was described; and (5) whether advance directives or similar written documents were referenced. Each item was coded dichotomously. We assessed inter-rater agreement between researchers using agreement rates and Cohen’s κ statistics.</p> Results <p>Of 116 identified judgments, 10 civil cases met the inclusion criteria. Patients had a mean age of 79.5 years, and all cases involved impaired decision-making capacity due to conditions such as dementia. Courts explicitly attempted to respect or infer patients’ wishes in two cases. Consideration of decision-making capacity and its medical assessment was noted in two cases. In two cases, courts treated family members’ wishes as sources for inferring the patient’s presumed wishes rather than as surrogate consent. A repeated, dialogical decision-making process was described in four cases. No judgment referred to advance directives. Inter-rater agreement was high for all items.</p> Conclusions <p>The civil court judgments analyzed in this study for patients with impaired decision-making capacity did not sufficiently reflect principles emphasized in ethical guidelines in Japan. This highlights an important challenge in clinical practice and medico-legal evaluation in Japan and underscores the need for future empirical research to evaluate the implementation of advance care planning in clinical practice.</p>