ADHD is often treated with stimulant medications, which have demonstrated short-term efficacy in numerous trials. However, treatment is often discontinued prematurely. Although ADHD often persists through adolescence, approximately half of all children who are treated with a stimulant medication discontinue treatment within one year (Charach, Ickowicz et al. 2004). Presumably, tolerability and treatment compliance are highly related to the side effect profile of stimulant medications (Schachar, Jadad et al. 2002). Sleep problems, particularly insomnia, are frequently associated with ADHD and are often exacerbated by stimulant medications, particularly at higher doses. Other frequent stimulant side effects are decreased appetite and mood lability (dysphoria/euphoria). Little is known about the relative effects of different stimulant formulations and dosages (i.e amphetamine, methylphenidate, dexmethylphenidate) on sleep and tolerability. There is some preliminary data with short acting stimulants suggesting a higher prevalence of sleep and appetite problems with amphetamine relative to mph (Pelham, Aronoff et al. 1999). Several studies indicate that sleep and other stimulant side effects are dose related (Stein, Sarampote et al. 2003), although this has not been found in all studies. Moreover, it is unclear if there are differences between long-acting amphetamine and methylphenidate based stimulants in their side effect profile and tolerability. Thus, we will directly compare these two long acting stimulant medications on their side effect profile and tolerability, including measures of sleep, mood, and evening behavior (e.g., family conflicts). The recently developed extended release formulation of dexmethylphenidate will be compared to one of the most common treatments for ADHD, extended release formulation of mixed amphetamine salts. The subject population will be older children and adolescents (10-17) with ADHD who are most likely to be treated with moderate to higher dose levels of stimulant medications and can complete all self-report measures.