Emotional dysregulation is the core feature of cyclothymia, and is present in up to 70% of ADHD patients. A growing body of research is showing a strong connection between cyclothymia and alterations in circadian rhythmicity, especially with evening chronotype and Delayed Sleep Phase Disorder (DSPD). Similar results have also been observed for ADHD. In this study we analysed a sample of ADHD and cyclothymic patients, evaluating their circadian preferences, their temperament, and their degree of emotional dysregulation. We then divided the sample among the ones with an extreme eveningness score, or having Delayed Sleep Phase Disorder (DSPD), and the others. We found a higher prevalence of cyclothymic temperament and measures of emotional dysregulation in the DSPD group.