Atypical antipsychotic drugs have less extra pyramidal side effects and are more effective to control the clinical manifestations of schizophrenia. However, their use may be associated to a higher incidence of weight gain, dyslipidemia, metabolic syndrome, glucose intolerance and type 2 diabetes mellitus. We performed a systematic literature search to evaluate the risk of type 2 diabetes mellitus incidence associated to the use of atypical antipsychotic drugs, compared to conventional treatment. If users of all types of atypical antipsychotic drugs are compared with users of conventional treatment, no significant differences in the incidence of type 2 diabetes mellitus were observed. If individual drugs are evaluated, clozapine and risperidone are associated with a higher risk of diabetes than haloperidol. Quetiapine is associated with a lower risk of diabetes than conventional treatment. The quality of the evidence found was low; therefore, new studies should been performed.