Affective instability in borderline personality disorder is due to a marked reactivity to environmental events. The present study focused on the relationship between affective instability and impulsivity in personality disorder. It used an experimental approach in the form of an affect-stimulation design based on the presentation of a short story which allowed for an analysis of affective responses in regard to quality, intensity, and alterations over time. Impulsive personalities showed a strong intensity of affective responses us well as a tendency towards rapid affect alterations supporting the theory of poor affect regulation in subjects with impulsive self-harming behaviour. Results suggest that affective instability is a crucial part of impulsive personality functioning.