Introduction Previous research has shown that Attention-Deficit Hyperactivity Disorder (ADHD) is linked to emotion dysregulation, but we still do not know enough about the specific nature of this deficit. The aim of the present study was therefore to study emotion dysregulation in adult ADHD using a new self-rating instrument, the Comprehensive Emotion Regulation Inventory (CERI). Methods The study included 390 participants, both adults diagnosed with ADHD and a comparison group. The CERI was created based on Gross process model of emotion. Unlike instruments already available, the CERI enables a detailed analysis of different strategies for regulating both positive and negative emotions and of the impact emotion dysregulation has on daily life. Results Results showed that the CERI has good psychometric properties, and a 5-factor solution was identified. Adults with ADHD differed from the comparison group with regard to how often they use different strategies, although effect sizes were small to medium. However, large effect sizes were found between ADHD and the comparison group with regard to problems implementing the use of various regulatory strategies and the negative impact on daily life functioning with regard to friendships, work/studies, or romantic relations. Within-group differences showed that adults with ADHD use the less advanced strategy suppression significantly more often compared to the more advanced strategies attentional deployment and reappraisal. Conclusions The CERI appears to be a valuable instrument for gaining more in-depth insights into emotion dysregulation in adults with mental disorders. Future research needs to examine what aspects of emotion dysregulation are shared between different mental disorders and what aspects might be specifically related to ADHD.