Background and Objectives: This study examines substance use disorder (SUD) treatment utilization patterns in response to a pandemic. Method: Retrospective electronic medical record data were collected during three time periods (N = 390): "Pre-COVID-19" (12/02/2019-03/14/2020), "COVID-19" (03/15/2020-06/30/2020), and COVID-19 "Re-entry" (7/01/2020-10/01/2020). Number of visits in each time period, SUD diagnosis, treatment modality (video, telephone, none), demographic, and clinical variables were examined. One-way analyses of variance (ANOVA) and chi-square analyses tested the relationships between treatment modality, demographics, clinical variables, and psychiatric emergency room (PER) visits. Binary logistic regressions examined the effect of treatment modality on PER use during COVID-19 and Re-entry, controlling for alcohol, opioid, and cocaine use disorders, age, and past-year (pre-COVID-19) PER use.Results: Treatment modality was associated with SUD (alcohol, cocaine, opioids), age, and PER visits. Veterans who primarily attended telephone appointments were more likely to require PER services compared to those attending video appointments. In the full model, alcohol use disorder (AUD), past-year PER visits, and treatment modality (telephone visits) continued to be significantly associated with COVID-19 PER use, while past-year PER visits correlated with Re-entry PER use.Conclusions and Scientific Significance: During COVID-19, veterans whose main treatment modality was telephone were more likely to require PER services than veterans who were seen by video, even after controlling for age, AUD, opioid use disorder, and past-year PER visits. This study is the first to have examined SUD treatment modality utilization patterns in response to COVID-19. Findings suggest that treatment modality during the initial phase of COVID-19 correlated with PER presentation.