Two studies examined the feasibility, utility, and validity of Ecological Momentary Assessment (EMA) and Recurrence Quantification Analysis (RQA) in assessing emotion dysregulation in children with Attention-Deficit/Hyperactivity Disorder (ADHD). In Study 1, 11 parents of children with ADHD ages 8-11 completed EMA-based ratings of their children's mood three times daily for 28 days (84 ratings total) and questionnaires regarding their children's emotion dysregulation. RQA was used to quantify the temporal patterning of dysregulation of the children's mood. In Study 2, five children ages 8-11 completed EMA-based ratings of their mood three times daily for 28 days. Results supported the feasibility and validity of the parent report EMA protocol, with greater intensity, variability, and persistent patterning of variability associated with greater emotion dysregulation. Results did not support the validity of the child report protocol, as children were less likely to complete ratings when emotionally distressed and demonstrated substantial response bias.