Background: Many children with asthma continue to experience symptoms despite available therapies. Objective: This study evaluated the efficacy and safety of omalizumab, a humanized anti-IgE mAb, in children with moderate-to-severe persistent allergic (IgE-mediated) asthma that was inadequately controlled despite treatment with medium-dose or high-dose inhaled corticosteroids (ICSs) with or without other controller medications. Methods: A randomized, double-blind, placebo-controlled trial enrolled children age 6 to < 12 years with perennial allergen sensitivity and history of exacerbations and asthma symptoms despite at least medium-dose ICSs. Patients were randomized 2:1 to receive omalizumab (75-375 mg sc, q2 or q4 wk) or placebo over a period of 52 weeks (24-week fixed-steroid phase followed by a 28-week adjustable-steroid phase). Results: A total of 627 patients (omalizumab, n = 421; placebo, n = 206) were randomized, with efficacy analyzed in 576 (omalizumab, n = 384; placebo, n = 192). Over the 24-week fixed-steroid phase, omalizumab reduced the rate of clinically significant asthma exacerbations (worsening symptoms requiring doubling of baseline ICS dose and/or systemic steroids) by 31% versus placebo (0.45 vs 0.64; rate ratio, 0.69, P = .007). Over a period of 52 weeks, the exacerbation rate was reduced by 43% versus placebo (P < .001). Omalizumab significantly reduced severe exacerbations. Over a period of 52 weeks, omalizumab had an acceptable safety profile, with no difference in overall incidence of adverse events compared with placebo. Conclusion: Add-on omalizumab is effective and well tolerated as maintenance therapy in children (6 to < 12 years) with mode rate-to-severe persistent allergic (IgE-mediated) asthma whose symptoms are inadequately controlled despite medium to high doses of ICSs. Q Allergy Clin Immunol 2009;124:1210-6.)