Objective: To investigate the effects of delayed and missed doses(poor compliance) on the pharmacokinetics of valproic acid(VPA) in epileptic children using Monte Carlo simulation.Methods: VPA time-concentration profiles in various scenarios are generated on epileptic children using Monte Carlo simulation, based on five published population pharmacokinetic studies [1-5].The scenarios include patients given multiple doses of VPA that ranged from 120mg to 500mg every 12h or 500mg and 750mg once a day.The therapeutic range of VPA for each scenario is estimated to assess the effects of delayed or missed doses and to design corresponding rescue regimens.Results: The risk for a sub-therapeutic range of VPA increase in a dose-dependent manner in both one and two times daily regimens when delayed or missed doses occurred.The effects of poor compliance are less prominent on the lower daily doses compared with those on the higher daily doses.The dose recommendations, in the event of poor compliance, are time related and dose dependent (Table 1).