OBJECTIVES: To examine the impact of atypical antipsychotic use on the persistence of long acting simulants (LAS) 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 study focused on children and adolescents aged 6 to 17 years, diagnosed with ADHD, and who initiated LAS after 6 months washout period. Concurrent use was defined as receipt of both medications together at least for 14 days. The persistence of LAS was defined as number of days to discontinuation of index LAS. The patients were censored at the discontinuation of index LAS or end of study period whichever comes first. Descriptive analysis was used to examine demographic, service related, and clinical characteristics of study sample. Accelerated Failure Time (AFT) regression was conducted to examine the determinants of persistence of LAS. RESULTS: Among the 61,793 children and adolescents who initiated LAS for ADHD 9,902 (16.03%) received LAS and atypical antipsychotic concurrently. Most of the study sample was children aged between 6-12 years, males, and whites. The mean duration of LAS treatment was longer (200 days) among concurrent users than only LAS users (143 days). The AFT regression found that concurrent users had 45% longer (STR, 1.45; 95% CI, 1.41-1.49) LAS persistence than those using LAS only. Adolescents and non-whites had shorter LAS treatment persistence than their counterparts after controlling for demographics, service related, and clinical factors.   CONCLUSIONS: The concurrent users had longer LAS treatment continuity than LAS only users. The addition of the atypical antipsychotic agents to LAS treatment may be beneficial in improving treatment persistence in ADHD.