Institutional betrayal occurs when the institutions that people depend on fail to protect them from harm, which was exemplified by a failure to manage COVID-19 risks. Inpatient psychiatry provides a rich context for which to understand the effects of institutional betrayal, and this is amplified in the context of the COVID-19 pandemic. Using a retrospective cohort design, we administered an online survey to former patients (n = 172) of inpatient psychiatry hospitalized at the height of the COVID-19 pandemic (March 2020 to February 2021) to understand the relationship between facilities’ use of COVID-19 mitigation activities (ie, offering or requiring face masks, keeping patients and staff 6 feet apart, access to hand sanitizer, use of telemedicine for clinical consults, and routine cleanliness of the unit) and former patients’ reports of institutional betrayal, changes in their trust in mental healthcare providers, fear of getting sick, and having contracted or witnessed someone else contract COVID-19. The quantity of COVID-19 mitigation activities was monotonically negatively associated with the probability of reporting any betrayal, the probability of reduced trust in mental healthcare providers, and the probability of being afraid of getting sick always or most of the time while hospitalized. COVID-19 mitigation activities either directly affected these psychological outcomes, or facilities that engaged in robust mitigation had greater cultures of safety and care quality. Additional qualitative work is needed to understand these mechanisms.