Stressful events due to the coronavirus disease-2019 (COVID-19) pandemic are likely to have profound effects on mental health, and validated methods for assessing these experiences and associations with psychopathology are needed. We developed the Pandemic Stress Questionnaire (PSQ) and tested its psychometric properties, characterized experiences in emerging adults, and examined associations with internalizing symptoms.Emerging adults (N = 450) completed the PSQ and measures of internalizing symptoms and perceived stress through an online platform in May 2020. One month later, 288 participants completed a follow-up questionnaire to assess reliability of the PSQ and longitudinal associations between stress and internalizing symptoms.Results supported the validity/reliability of PSQ total scores and indicated that stressful events were highly prevalent in May, particularly among younger, female, and Black emerging adults. Symptoms of depression and anxiety were high overall, but decreased at the follow-up assessment. Pandemic-related stress was moderately associated with both depression and anxiety at each assessment, but baseline stress did not predict change in symptoms when controlling for baseline symptoms.Results provide empirical evidence that emerging adults are at high risk for depression and anxiety related to the psychosocial effects of the COVID-19 pandemic, and highlight specific types of experiences associated with greatest risk. Further, this study provides support for a questionnaire measure of experiences related to the COVID-19 pandemic that can be applied in future work to advance understanding of risk and resilience in response to stressful events.