Thirty-day readmissions are a major concern for hospitals. Even though numerous readmission risk prediction models have been developed, their performance has been modest, and few predictors are modifiable. Stress is a modifiable factor that may increase risk of adverse post-hospitalization outcomes. We examined whether posttraumatic stress days after evaluation for acute coronary syndrome (ACS)—termed acute stress disorder (ASD) symptoms—was associated with 30-day all-cause emergency department (ED) and hospital readmission.Participants were enrolled in the REactions to Acute Care and Hospitalization (REACH) study during ED evaluation for ACS. During inpatient stay or by phone after discharge, participants reported ASD symptoms in response to the event that brought them to the ED. ED or hospital readmissions within 30days of discharge were determined by research nurse record review. Logistic regression was used to assess the association between ASD symptoms and 30-day ED/hospital readmission.In the analytic sample of 974 individuals, there were 123 ED/hospital readmissions within 30days of discharge. A 10-point ASD symptom increase was significantly associated with increased 30-day readmission risk in an unadjusted model [odds ratio (OR)=1.32, p=0.001] and a model adjusted for demographics, clinical characteristics, and ACS discharge diagnosis (OR=1.24, p=0.03).Posttraumatic stress shortly after acute coronary syndrome evaluation may help to understand vulnerability for readmission.