<h3>Introduction</h3> There are sex-related disparities in asthma. Before puberty, males have increased prevalence and severity of asthma compared with females, and this pattern reverses after the onset of puberty. Omalizumab, an IgE antibody, is an effective treatment for allergic asthma, but sex-specific responses have not been studied in detail. <h3>Methods</h3> Post hoc analysis examined data from randomized, placebo-controlled IA05 trial of omalizumab treatment (52 weeks; 75-375 mg sc every 2-4 weeks; N=627; 6 to <12 years, ie children) and open-label, single-arm PROSPERO study (NCT01922037; 48-weeks; N=801; ≥12 years ie adolescents/adults (n=732 ≥18 years); both included patients with moderate-severe allergic asthma. <h3>Results</h3> In IA05/PROSPERO, baseline characteristics of mean age and IgE levels were similar for female and male participants (females 8.4/47.8 versus males 8.6/46.2 years; IgE levels females 463.2/560.3 versus males 472.8/615.0 IU/mL). Asthma exacerbation rates following omalizumab treatment were similar for females and males. In IA05 (children), asthma exacerbation rates were: females - placebo 0.74 versus omalizumab 0.46, males - placebo 0.55 versus omalizumab 0.43, and the interaction test of effect of sex on omalizumab response was not significant (p=0.4821). In PROSPERO (adolescents/adults), asthma exacerbation rates in females were 0.74 versus males 0.77 (p=0.787). Overall safety reported previously for IA05, Lanier JACI 2009;124;1210-6 and PROSPERO, Casale JACI:IP 2019;7(1):156-64. <h3>Conclusions</h3> Despite differences in asthma between females and males, we found no evidence that the effect of omalizumab in children was dependent on sex, and no evidence that the rate of exacerbations was dependent on sex following omalizumab initiation in adolescents/adults.