It has been increasingly recognized that antipsychotic agents might cause a number of metabolic effects such as obesity, dyslipidemia, diabetes mellitus and hyperleptinemia. Antipsychotic drugs have also been reported to be associated with venous thromboembolism (VTE).The highest risk of VTE emerges during the ?rst 3 months after initiation of treatment. Potential etiopathogenetic factors leading to VTE during treatment with antipsychotic agents include sedation, obesity, elevation of antiphospholipid antibodies, increased platelet activation and aggregation, hyperhomocysteinemia, and hyperprolactinemia. While an increased risk of VTE has been associated with first-generation low- potency antipsychotic agents, particularly clozapine, there appears to be a growing number of reports on the occurrence of this adverse reaction during the use of second-generation antipsychotics, such as risperidone and olanzapine. No case reports are available in the literature about the occurrence of VTE in patients treated with a ‘metabolically gentler’ antipsychotic such as ziprasidone and aripiprazole. In this case report, we discussed DVT complication in a mild mentally retarded adolescent with Klinefelter syndrome after administration of aripiprazole for the treatment of behavioural problems.