ImportanceAlthough substantial research has reported grave population-level psychiatric sequelae of the COVID-19 pandemic, evidence pertaining to temporal changes in schizophrenia spectrum disorders in the US following the pandemic remains limited.ObjectiveTo examine the monthly patterns of emergency department (ED) visits for schizophrenia spectrum disorders after the onset of the COVID-19 pandemic.Design, Setting, and ParticipantsThis observational cohort study used time-series analyses to examine whether monthly counts of ED visits for schizophrenia spectrum disorders across 5 University of California (UC) campus health systems increased beyond expected levels during the COVID-19 pandemic. Data included ED visits reported by the 5 UC campuses from 2016 to 2021. Participants included persons who accessed UC Health System EDs had a diagnosis of a psychiatric condition. Data analysis was performed from March to June 2023.ExposuresThe exposures were binary indicators of initial (March to May 2020) and extended (March to December 2020) phases of the COVID-19 pandemic.Main Outcomes and MeasuresThe primary outcome was monthly counts of ED visits for schizophrenia spectrum disorders. International Statistical Classification of Diseases and Related Health Problems, Tenth Revision diagnosis codes, categorized within Clinical Classification Software groups, were used to identify ED visits for schizophrenia spectrum disorders and all other psychiatric ED visits, from the University of California Health Data Warehouse database, from January 2016 to December 2021. Time-series analyses controlled for autocorrelation, seasonality, and concurrent trends in ED visits for all other psychiatric conditions.ResultsThe study data comprised a total of 377 872 psychiatric ED visits, with 37 815 visits for schizophrenia spectrum disorders. The prepandemic monthly mean (SD) number of ED visits for schizophrenia spectrum disorders was 519.9 (38.1), which increased to 558.4 (47.6) following the onset of the COVID-19 pandemic. Results from time series analyses, controlling for monthly counts of ED visits for all other psychiatric conditions, indicated 70.5 additional ED visits (95% CI, 11.7-129.3 additional visits; P = .02) for schizophrenia spectrum disorders at 1 month and 74.9 additional visits (95% CI, 24.0-126.0 visits; P = .005) at 3 months following the initial phase of the COVID-19 pandemic in California.Conclusions and RelevanceThis study found a 15% increase in ED visits for schizophrenia spectrum disorders within 3 months after the initial phase of the pandemic in California across 5 UC campus health systems, underscoring the importance of social policies related to future emergency preparedness and the need to strengthen mental health care systems.