Previous research has shown that in response to a monotonous, boring lab situation, non-clinical participants voluntarily self-administer electric shocks. The shocks probably served to disrupt the tedious monotony: they were the only available external source of stimulation. Alternatively, the shocks might have functioned to regulate the negative emotional experience caused by the induction of boredom, consistent with theories on the function of non-suicidal self-injury (NSSI). According to this latter explanation, induction of other negative emotions would also increase the administration of shocks. To test this explanation, 69 participants watched a monotonous, sad or neutral film fragment, during which they could self-administer electric shocks. Participants in the boredom condition self-administered more shocks and with higher intensity, compared to both the neutral and sadness condition. Sadness had no effect on the self-administration of shocks. The effect of boredom was more pronounced in participants with a history of NSSI: they administered more shocks in the first 15 min. The results indicate that the shocks function to disrupt monotony and not to regulate negative emotional experience in general. Moreover, boredom appears an important impetus for NSSI.