OBJECTIVE Aripiprazole is a new generation antipsychotic drug that shows a partial agonistic activity at D(2) and 5-HT(1A) receptors. This might lead in some cases to an exacerbation of psychotic symptoms due to dopamine agonism. METHODS We report the case of a 39-year-old woman with an ICD-10 defined schizoaffective disorder. RESULTS Risperidone was started to treat psychotic symptoms. Psychotic symptoms disappeared but because of galactorrhoea risperidone needed to be discontinued. Subsequently, an antipsychotic treatment regimen with aripiprazole and haloperidol was prescribed. After initiating aripiprazole and haloperidol the patient's psychotic symptoms increased drastically. Therefore aripiprazole and haloperidol were discontinued. Olanzapine was prescribed and psychotic symptoms declined again. CONCLUSIONS Concurrent causes for this serious adverse event may be the partial agonistic activity of aripiprazole at D(2) receptors as well as an up-regulation of dopamine receptors during prior treatment with risperidone. Both aspects may have contributed to the severe psychotic exacerbation. Clinicians should be aware of this possible, serious adverse event while switching to aripiprazole or prescribing aripiprazole with other antipsychotics. Because of their lower D(2) receptor affinity quetiapine and clozapine might be a better choice for combined treatment with aripiprazole.