Aripiprazole is an atypical antipsychotic agent with an intrinsic dopamineagonist activity of 30 %. Aripiprazole exerts additional partial agonist action on 5-HT (1A) receptors and has antagonist properties at 5-HT (2A) receptors. Controlled studies demonstrated an effectiveness in acute relapse of schizophrenic psychosis, chronical schizophrenic and schizoaffective disorders. Aripiprazole was effective in the treatment of productive psychotic and negative symptoms. Compared to other antipsychotics aripiprazole demonstrated a favourable profile of side effects: only slight changes of body weight, mild extrapyramidal symptoms, no prolactin elevation and no significant changes in QTc interval. The efficacy in the long term treatment of schizophrenia seems to be similar to other antipsychotics (e. g. olanzapine). The first evaluations of studies with patients with bipolar disorders showed a significant efficacy in the treatment of mania.