OBJECTIVES: The study examined cardiovascular safety of concurrent atypical antipsychotic agents and long acting stimulants (LAS) use in children and adolescents with Attention Deficit/Hyperactivity Disorder (ADHD). METHODS: The study involved retrospective longitudinal analysis of 2003-2007 Medicaid Analytical eXtract (MAX) data of four US states. The cohort involved children and adolescents aged 6 to 17 years who initiated treatment with LAS for ADHD. The continuous eligibility 6 months before and 12 months after the index LAS date was ensured for the study cohort. Atypical antipsychotic use was identified after the initiation of the index LAS and classified as current use (days of active use), former use (days after current use), and nonuse (time before the first use including the follow up of those who never exposed to atypicals). The study end point was defined as the first inpatient or outpatient claim due to cardiovascular event. The risk for cardiovascular event was evaluated   using time dependent Cox regression analysis.  RESULTS: All the study participants were followed for 9,206,873 person-days of observation period. The numbers of cardiac events were 840, 202, and 45 during periods of atypical non-use, current use, and former use respectively. After controlling for demographic, service related, and clinical characteristics, the study found that current users and  former users of atypical antipsychotics were not associated with cardiovascular events compared to no atypical users (Current use: HR, 1.17, 95% CI, 0.98-1.40; Former use: HR, 1.24; 95% CI, 0.91-1.69). However, patient characteristics like diagnosis of obesity and diabetes, and use of mood stabilizers increased the risk of cardiovascular events. CONCLUSIONS: The study did not find any increased cardiovascular risk with addition of the atypical antipsychotics to long acting stimulant regimen in children and adolescents diagnosed with ADHD.