Determinants of Unpaid Hospital Charges Among Non-Resident Foreign Patients: A Retrospective Single-Center Study in Tokyo, Japan

<b>Background/Objectives</b>: Unpaid medical expenses incurred by foreign nationals represent a growing concern for healthcare systems amid increasing international mobility. Japan, which lacks mandatory public insurance coverage for non-resident visitors, faces particular vulnerability in terms of uncompensated hospital care. This study aims to identify factors contributing to unpaid medical charges among uninsured, non-resident foreign patients hospitalized at a tertiary care facility in Tokyo. <b>Methods</b>: This retrospective observational analysis was conducted using medical and administrative data from patients admitted between January 2023 and February 2025. Patients who received elective medical tourism care were excluded. Data on demographics, length of hospital stay, care intensity, payment status, and third-party financial assistance were analyzed. Logistic regression models were applied to assess predictors of nonpayment. <b>Results</b>: Among 153 eligible cases, 9 patients (5.9%) had outstanding hospital bills upon discharge. Compared with those with completed payments, the unpaid group experienced longer admissions, more intensive care utilization, and higher total charges. Notably, the absence of third-party financial support (primarily travel insurance) was significantly associated with unpaid charges. Multivariate analysis identified this factor as the main independent predictor (adjusted odds ratio [OR]: 0.12; 95% confidence interval [CI]: 0.02-0.915; <i>p</i> = 0.040). Total amount of billing was also statistically significant (adjusted odds ratio [OR]: 1.01; 95% confidence interval [CI]: 1.00-1.01; <i>p</i> = 0.039). <b>Conclusions</b>: These findings highlight the importance of private insurance in mitigating financial risk in hospitals. Implementing policy measures to promote or require insurance enrollment, along with streamlined reimbursement systems, may contribute to sustainable care delivery for international patients.