The increasing use of olanzapine for treating adolescent patients has brought with it greater awareness of the recognized side effects of this medication, especially weight gain. Of the reports of glucose dysregulation related to olanzapine therapy, only a few pertain to adolescents. We present five cases: two youths who consequently suffered from overt diabetes and three who responded with glucose dysregulation. According to the Naranjo probability scale, the relation of this phenomenon to olanzapine therapy is "probable." We consider the findings of the presented case series as justification for regular metabolic follow-up for apparently healthy adolescents receiving olanzapine therapy.