Objective: To describe symptom rebound in children with ADHD treated with lisdexamfetamine dimesylate (LDX) or placebo. Method: During a 4-week, randomized, double-blind, placebo-controlled trial of LDX, parents/caregivers completed the Conners’ Parent Rating Scale–Revised: Short Form symptom rating scale throughout the day. Response, rebound, and emotional lability (EL) were assessed post hoc based on predefined criteria. Results: Most participants given LDX (n = 207) were responders throughout the day (50.7%-55.6%) versus placebo (n = 72; 11.1%-22.2%). A total of seven (3.4%) LDX participants showed rebound in the afternoon and/or evening versus seven (9.7%) with placebo. In both groups, most incidences of rebound occurred in the evening. EL (mean) was higher in LDX rebounders and nonresponders (range = 4.2-9.0) versus LDX responders (range = 1.3-1.6) and versus placebo rebounders (range = 0.7-1.9). Conclusion: ADHD symptom rebound occurred in few participants (3.3%) given LDX (accompanied by clinically significant EL). Overall, more participants given LDX versus placebo responded throughout the day. (J. of Att. Dis. 2012; XX(X) 1-XX)