This review provides a meta-analysed male:female prevalence ratio of oppositional defiant disorder (ODD) during middle childhood in non-referred children. It also analyses sex differences in prevalence across cultures and over time. A systematic search for studies via the following sources was conducted: PsycInfo, Web of Knowledge, Medline Complete, Scopus, EMBASE, InfoRMIT, Psychological and Behavioural Sciences Collection, Cochrane Library, PubMed and ProQuest Health. The studies presented in two previous systematic reviews were also added to the search results. Inclusion/exclusion criteria were then applied and final studies were appraised for their methodological quality. Nineteen independent effect sizes met full inclusion criteria (aggregated sample N = 44,107). Overall, the prevalence of ODD was significantly higher in boys than girls (RR = 1.59, 95 % CI [1.36, 1.86], p < 0.001), with the male:female prevalence ratio found to be 1.59:1. Sex differences in prevalence were significant in Western (RR = 1.80, 95 % CI [1.55, 2.10], p < 0.001) but not non-Western cultures (RR = 1.08, 95 % CI [0.76–1.53], p > 0.05). Sex differences in prevalence were significant in studies published prior to and post the year 2000 (RR = 1.57, 95 % CI [1.22, 2.02], p < 0.001; RR = 1.64, 95 % CI [1.35, 2.00], p < 0.001), and were consistent between these two periods (Q, 1 = 0.36, p = > 0.05). The sex differences in ODD prevalence are discussed within the context of (i) predominant theories of sex differences in externalising behaviours, and (ii) departure from the sex-differences pattern found for other disruptive behavioural disorders.