OBJECTIVES: This study investigates the healthcare costs of adverse events (AE) associated with treatment of bipolar disorder with two atypical antipsychotics (AA): aripiprazole (ARI) and Olanzapine (OLA). METHODS: It was performed a cost analysis through a markov model considering the following health states: no existence of adverse events (NAE); extrapyramidal symptoms (EPS); weight gain (WG); and sexual dysfunction (SD). The transition probabilities amongst health states were estimated from two different meta-analysis of  clinical trials and from a retrospective Spanish study. The health care costs associated to each health state were obtained from a published Spanish study. It was used the minimum acquisition cost per mg. of the mean daily dose, for each AA, which is regarded as a relevant efficiency criterion in Hospital Pharmacy Departments. The time horizon applied in the analysis was 12 months. A probabilistic sensitivity analysis was performed for all the variables involved in the analysis via Monte Carlo simulations. All costs were inflated to 2009 costs using Spanish Health System pay and prices index. RESULTS: In comparison with OLA, the treatment with ARI generates annual average cost savings per patient of €-688.70±21.69 (CI95% -614.52; -729.18). In the most unfavourable scenario for ARI, that in which we assumed that ARI may have a similar rate of sexual dysfunction than that of quetiapine (i.e. the lowest rate amongst AA) the costs savings per patient would be €-270,94±17,11 (CI95% -237,20; -303,48). CONCLUSIONS: The results of this analysis show that patients treated with aripiprazole demonstrate lower adverse events costs in comparison to olanzapine. This difference may generate significant cost savings to the Spanish health system in the treatment of patients affected by bipolar disorders. The robustness of the results was tested via a probabilistic sensitivity analysis.