Intensive care unit healthcare workers (ICU HCW) are at risk of mental health issues during emerging disease outbreaks. A study of ICU HCW from France revealed symptoms of anxiety and depression in 50.4% and 30.4% of workers at the peak of the first wave of the pandemic. The level of COVID-19 exposure of these ICU HCW was very high. In Canada, ICU HCW experienced variable exposure to COVID-19 during the first wave of the pandemic, with some hospitals seeing large numbers of patients while others saw few or none. In this study we examined the relationship between COVID-19 exposure and mental health in Canadian ICU HCW. We conducted a cross-sectional cohort study of Canadian ICU HCW in April 2020, during the acceleration phase of the first wave of the pandemic. Psychosocial distress was assessed using the 12-item General Health Questionnaire (GHQ-12). Participants were asked about sources of stress as well as about exposure to COVID-19 patients and availability of personal protective equipment (PPE). Factors associated with clinically-relevant psychosocial distress were identified. Responses were received from 310 Canadian ICU HCW affiliated with more than 30 institutions. Of these, 64.5% scored ≥ 3 points on the GHQ-12 questionnaire, indicating clinically-relevant psychosocial distress. The frequency of psychosocial distress was highest amongst registered nurses (75.7%) and lowest amongst physicians (49.4%). It was also higher amongst females (64.9%) than males (47.6%). Although PPE availability was good (> 80% of participants reported adequate availability), there was significant anxiety with respect to PPE availability, with respect to the risk of being infected with COVID-19, and with respect to the risk of transmitting COVID-19 to others. In multivariable regression analysis, Anxiety with respect to being infected with COVID-19 (OR 1.53, CI 1.31-1.81) was the strongest positive predictor of clinically-relevant psychosocial distress while the Number of shifts with COVID-19 exposure (OR 0.86, CI 0.75-0.95) was the strongest negative predictor. In summary, clinically-relevant psychosocial distress was identified amongst a majority of ICU HCW during the acceleration phase of the first wave of the COVID-19 pandemic, including those with minimal or no exposure to COVID-19. Strategies to support mental health amongst ICU HCW are required across the entire healthcare system.