Importance: The outbreak of the novel coronavirus (COVID–19) has challenged the capacity of healthcare systems around the world and can potentially compromise healthcare utilization and health outcomes among non-COVID–19 patients. However, the empirical evidence regarding changes in healthcare utilization, healthcare spending, and health status among non-COVID–19 patients is limited. Objective: To examine the associations of the COVID-19 pandemic with healthcare utilization, out-of-pocket medical costs, and perceived health status in Singapore. Design: A retrospective observational study using a difference-in-differences method that examines changes in healthcare utilization, healthcare spending, and perceived health status before and during the outbreak of COVID-19 of the same individuals using monthly individual-level panel survey data. Setting: Singapore between June 2018 and June 2020. Participants: Singaporeans aged 50–70 (N=7,569; January 2020). Exposures: Outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in January 2020 in Singapore. Main Outcomes and Measures: Healthcare utilization, diagnosis of chronic health conditions, out-of-pocket medical costs (total and by medical service categories), self-reported measures of overall health status, sleep quality, and depressive symptoms. Results: Of 7,569 sample respondents in the January 2020, 53% are female, and 87% are ethnic Chinese. Their average age was 63.2. Between January and April 2020, COVID-19 was associated with a decrease in doctor visits by 9.3 percentage points (31% reduction from 29.8%; 95% Confidence Interval (CI), -11% to -8%). It was also associated with a decrease in out-of-pocket medical spending by S$46.5 (23% reduction from S$198 in January 2020; 95% CI, -S$74.3 to -S$18.7), mostly driven by reductions in inpatient and outpatient care, and a decrease in the probability of any diagnosis of chronic conditions by 2.7 percentage points (19% reduction from 13.9%; 95% CI, -4% to -2%). Although there were little changes in self-reported health status and sleep quality, COVID–19 was associated with an increase in depressive symptoms by 2.8 percentage points (4% reduction from 71%; 95% CI, 1.1% to 4%). Conclusions and Relevance: It is imperative to monitor COVID–19’s long-term health effects among non-COVID–19 patients since our findings indicated delayed healthcare and worsened mental health related to the outbreak.