The Positive and Negative Affect Schedule (PANAS) has been widely used to assess affect expression. Shortened and adolescent versions of the measure have been created, such as the 10-item PANAS for Children (PANAS-C). However, affect expression often involves substantial intraindividual variability, and no research has examined within-person differences using the 10-item PANAS-C. Moreover, intraindividual variability is a key characteristic of attention-deficit hyperactivity disorder (ADHD), and emotion dysregulation is a key feature of ADHD. The present study examined the factor structure of the 10-item PANAS-C in a sample of adolescents (M[subscript age] = 13.17 years) with (n = 156) and without (n = 139) ADHD. A 3-factor (Positive Affect, Fear, Distress) within and a 2-factor (Positive Affect, Negative Affect) between model was found to be best fitting using both parent- and adolescent-report. The model demonstrated configural invariance for the adolescent-report and scalar invariance for the parent-report. These results support the multidimensionality of negative affect in youth with ADHD, even when assessed via the short-version PANAS-C. In future work, it will be important to consider the implications of more discrete types of negative affect expression (fear and distress) found across time at the individual level for assessment and intervention practice. [This paper will be published in "Psychological Assessment."]