BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has had a profound impact on health care utilization. However, the overall picture of shifts in health care utilization remains unclear. OBJECTIVE: We assessed the ecology of medical care during the COVID-19 pandemic in Japan and compared it with the results pre-pandemic. We also investigated the associations of sociodemographic and clinical factors with health care utilization during the COVID-19 pandemic. DESIGN AND METHODS: We conducted a nationwide cross-sectional survey of a representative sample of the general Japanese adult population in May 2021. The main outcomes were health care utilization for health-related events in the last month. We assessed sociodemographic and clinical factors, including age, sex, years of education, annual household income, social isolation, and the number of chronic conditions. KEY RESULTS: Data were analyzed from 1747 respondents. Over-the-counter drug use, physician's office visits, and hospital outpatient clinic visits decreased drastically during the COVID-19 pandemic compared with pre-pandemic levels. The decrease in the use of medical facilities was especially pronounced among the elderly. Sociodemographic and clinical factors were differently associated with health care utilization during the COVID-19 pandemic. Social isolation and years of education were positively associated with over-the-counter drug use, while female sex was associated with increased over-the-counter drug use and physician's office visits. In addition, the number of chronic conditions was associated with increased hospital visits. CONCLUSIONS: During the COVID-19 pandemic, the use of medical facilities for health-related events decreased drastically, especially among the elderly. A pharmacy is an important source of health care in a population with social isolation. These findings may be useful to researchers and policymakers in rethinking health care systems during and after the pandemic.