Introduction: The increasing burden of non-communicable diseases and limited public financing are major challenges facing health care systems in Latin America. Although COVID-19 severely impacted the Brazilian health care system, it is crucial to further characterize the degree of disruption caused to public health efforts, in order to address and manage long term effects of this pandemic. We therefore quantified the demand for preventive and treatment services from the Brazilian Unified Health System (Sistema Único de Saúde/SUS) in 2020 to evaluate potential repercussions of COVID-19 in this setting. Methods: Using the SUS database, we compared preventative and treatment services rendered in 2020 to the same services rendered from 2017 to 19. We also evaluated the frequency of respiratory infection (RI) diagnoses during the pandemic, relative to the preceding years. Results: Compared to 2017-19, in 2020 non-urgent medical appointments decreased 1.4-fold (p = 0.0017), dental consultations 2.8-fold (p = 0.05), and immunization coverage 1.5 fold (p = 0.0005). The number of RI visits to SUS ambulatory care units in 2020 was 4.2 times higher than in preceding years (p = 0.0014), with a peak of 280,898 diagnoses in July 2020. Conclusion: The COVID-19 pandemic appears to have led to a dramatic decline in preventative and treatment services provided by SUS to the Brazilian population. Our findings may aid decision-makers in formulating policies to increase the availability of outpatient services in the aftermath of the pandemic. Counter measures will be critical to avoid a resurgence in vaccine-preventable diseases and complications stemming from non-communicable, chronic health conditions.