Interruptions are part of everyday life and are known to be disruptive. With, the current study we investigated which kind of interruption is more disruptive: external interruptions or self-interruptions. We conducted two experiments, one behavioral experiment (28 participants) and one in which pupil dilation was measured (21 participants). In both experiments, self-interruptions made participants complete the main task slower than external interruptions (occurring at similar moments in the task as the self-interruptions). However, there was no difference between the two kinds of interruptions in the time needed to resume the main task (resumption lag). Instead, the pupil dilation data revealed that the decision to self-interrupt takes about 1 s, resulting in slower performance overall. (C) 2016 Elsevier Ltd. All rights reserved.