Correct classification of irritability is extremely important to assess prognosis and treatment indications of juvenile mood disorders. We assessed factors associated with low versus high parent- and self-rated irritability using the affective reactivity index (ARI) in a sample of 289 adolescents diagnosed with a bipolar or a major depressive disorder. Bivariate analyses were followed by multilinear logistic regression model. Factors significantly and independently associated with high versus low parent-rated ARI score were: more severe emotional dysregulation and bipolar disorders diagnosis. Factors significantly and independently associated with high versus low self-rated ARI score were: lower children depression rating scale (CDRS-R) difficulty of having fun item score, greater children depression inventory (CDI-2) self-report score, more severe emotional dysregulation, and greater CDRS-R appetite disturbance item score. High parent-rated irritability was strictly related with a bipolar disorder diagnosis, whereas high youth-rated irritability was related to depressive phenotype characterized by appetite/food-intake dysregulation, mood lability, and less anhedonia and apathy.