Increasing epidemiological evidence suggests that environmental stressors such as trauma and life events are associated with the development of psychosis. The underlying mechanism however remains unclear. Previous studies of our group have demonstrated that increased sensitivity to daily life stress is part of the underlying vulnerability for psychosis. It is therefore attractive to hypothesize that early trauma increases the risk for psychosis through sensitizing people for the small stresses of daily life. This hypothesis has been investigated in three different data sets (both general-population and clinical samples) using the Experience Sampling Method (ESM; a structured diary technique) to assess stress-reactivity in daily life defined as emotional and psychotic reactivity to stress. The results suggest that a history of childhood trauma sensitizes people to the stresses of normal life resulting in stronger emotional and psychotic reactions to stress. However, this sensitization process is most pronounced in subjects with an increased vulnerability for psychosis.