Background <p>Delirium occurs in 10%–30% of older hospitalized adults and is associated with adverse events and medical dispute risk. This study investigated patterns of delirium-related adverse events and medical disputes in Japan.</p> Methods <p>We conducted an exploratory comparative analysis of adverse events from the Japan Council for Quality Health Care (<i>n</i> = 743) and closed medical dispute claims from a major medical malpractice insurer in Japan (<i>n</i> = 32) from 2017 to 2021. Failure modes were classified according to the World Health Organization International Classification for Patient Safety and analyzed using Fisher’s exact test and Firth’s bias-reduced logistic regression.</p> Results <p>Management failures occurred in 92.7% of adverse events but only 50.0% of claims. The distribution of failure modes differed between the groups (<i>p</i> &lt; 0.001). Diagnosis and medication failures occurred in 4.3% of adverse events but accounted for 37.5% of claims. Mortality was higher among closed claims (31.3%) than adverse events (6.7%) (<i>p</i> &lt; 0.001). Non-management failures showed higher liability (62.5% vs. 43.8%, OR = 2.14, 95% CI: 0.55–8.29) and litigation rates (18.8% vs. 6.3%, OR = 3.50, 95% CI: 0.32–37.9) compared to management failures, although statistical significance was not achieved, possibly due to small sample sizes.</p> Conclusions <p>National adverse event reports and closed claims captured different aspects of delirium-related harm. Management events predominated in adverse event reports, whereas diagnostic and medication-related failures were more visible in closed claims than in adverse event reports. These exploratory findings support using complementary data sources to inform delirium safety strategies.</p> Trial registration <p>Not applicable.</p>