Patients with schizophrenia or bipolar disorder treated with antipsychotic medication can frequently experience lack of efficacy and persistent side-effects, so much so that switching from one antipsychotic to another with a different side-effect profile has become a recommended strategy for improving the tolerability and safety of long-term antipsychotic treatment. Aripiprazole is an atypical antipsychotic with proven efficacy in schizophrenia and bipolar I disorder, with a pharmacological profile distinct from other available antipsychotics and a side-effect profile that is different from other agents in the class; these characteristics make it a possible alternative in patients requiring a change in antipsychotic treatment due to lack of efficacy or persistent side-effects.