AbstractPurpose:The aim of the current study was to replicate findings in adults indicating that higher sensitivity to stressful events is predictive of both onset and persistence of psychopathological symptoms in a sample of adolescents and young adults. In addition, we tested the hypothesis that sensitivity to mild stressors in particular is predictive of the developmental course of psychopathology.Methods:We analyzed experience sampling and questionnaire data collected at baseline and one-year follow-up of 445 adolescent and young adult twins and non-twin siblings (age range: 15–34). Linear multilevel regression was used for the replication analyses. To test if affective sensitivity to mild stressors in particular was associated with follow-up symptoms, we used a categorical approach adding variables on affective sensitivity to mild, moderate and severe daily stressors to the model.Results:Linear analyses showed that emotional stress reactivity was not associated with onset (ß = .02; P = .56) or persistence (ß = -.01; P = .78) of symptoms. There was a significant effect of baseline symptom score (ß = .53; P < .001) and average negative affect (NA: ß = .19; P < .001) on follow-up symptoms. Using the categorical approach, we found that affective sensitivity to mild (ß = .25; P < .001), but not moderate (ß = -.03; P = .65) or severe (ß = -.06; P = .42), stressors was associated with symptom persistence one year later.Discussion:We were unable to replicate previous findings relating stress sensitivity linearly to symptom onset or persistence in a younger sample. Whereas sensitivity to more severe stressors may reflect adaptive coping, high sensitivity to the mildest of daily stressors may indicate an increased risk for psychopathology.