This workshop provides a summary of the phenomenology, course, and treatment of ADHD and bipolar disorder. Dr. Carlson discusses the reasons for confusion between bipolar disorder and ADHD in pediatric settings by demonstrating ways in which the same symptom can have different interpretations. In addition, she clarifies the definition of mood dysregulation. Throughout the workshop, she describes assessment considerations and materials to adequately assess ADHD, severe mood dysregulation, manic-like symptoms, and bipolar disorder. She provides details on the Child/Adolescent Symptom Inventory (CASI) and the Child Mania Rating Scale (C-MRS). Dr. Carlson also presents example cases to discuss differential diagnosis. Lastly, she discusses the treatment implications for a variety of presenting symptoms.