Atypical or second-generation antipsychotic agents, such as aripiprazole and olanzapine, are increasingly used in the management of schizophrenia and bipolar disorders in children. The atypical antipsychotic agents have been associated with the development of hyperglycemia, ketoacidosis, and diabetes. The mechanism of atypical antipsychotic-mediated hyperglycemia is unclear. Most of the published reports have been on individuals at risk for type 2 diabetes. We present the first known cases of the development of diabetes and positive glutamic acid decarboxylase antibodies (suggestive of autoimmune diabetes) in adolescents while on treatment with atypical antipsychotics. The nature of their clinical presentations and the time course of antipsychotic therapy to clinical diagnosis of diabetes make us speculate that atypical antipsychotics may shorten the time course of the development of autoimmune diabetes in predisposed children.