Introduction: Kawasaki disease (KD), first reported in 1967, is a risk for ischemic heart disease if complicated by coronary sequelae. However, limited information is available regarding the follow-up status and outcomes of adults hospitalized for severe coronary sequelae resulting from KD. Hypothesis: We hypothesize that emergency or non-referral admission is related to poor outcomes in adults with KD hospitalized for severe coronary sequelae. Methods: Using a nationwide claim-based dataset from Japan, we analyzed adult patients (aged 15 and above) with KD diagnosed according to ICD10 codes, who were hospitalized for the treatment of coronary artery sequelae between April 2013 and March 2020. Treatment groups included acute coronary syndrome (ACS), catheter intervention (PCI), coronary artery bypass grafting (CABG), or the heart failure/arrhythmia group (patients treated for heart failure or arrhythmia, excluding those in the other three groups). ACS was diagnosed based on ICD-10 codes, while other diagnoses were determined using specific procedures. Results: The study comprised 850 patients, predominantly male (74%), with a median age of 34 years (IQR:20-43) and a median body mass index of 22.5 (IQR:20.0-25.4). They were divided into four groups: ACS (n=112), PCI (n=86), CABG (n=92), and the heart failure/arrhythmia group (n=560). The overall patient cohort had emergency admissions (27%) and non-referral admissions (13%), as well as heart failure (46%) and arrhythmia treatment (84%). Outcome measures included intensive care unit care (24%), median hospitalization duration of 4 days (IQR:3-13), total hospital deaths (1%), and median direct medical fees (4932600 Japanese yen). A higher percentage of emergency or non-referral admissions in the ACS or the heart failure/arrhythmia group correlated with unfavorable outcome parameters (p<.05). Conclusions: The present nationwide claim-based dataset study of adults hospitalized for severe coronary sequelae following KD, characterized by young males with normal BMI, showed that emergency or non-referral admission is associated with poor outcomes in the ACS and heart failure/arrhythmia groups. These findings support the importance of healthcare transition for such patients with KD.