Epidemiological studies on autism lack representation from Asia. We estimated the prevalence of autism among children and youths in Hong Kong using a two-stage approach. In addition, we evaluated the psychometric properties of the screening instrument and explored sex differences within an epidemiological context. A random school-based sample of 5,865 children and youths were screened with the Autism Spectrum Quotient-10 (AQ-10). Then, a subsample of 317 participants underwent the Autism Diagnostic Interview-Revised assessment. Prevalence was estimated by applying positive and negative predictive values (PPV/NPV) of AQ-10 derived from the subsample to the entire cohort. None of the screened negative participants had autism, resulting in an NPV of 100%. Discrepant PPVs were noted for males (20.4%) and females (5.20%). The estimated prevalence was 2.57% using sex-specific PPVs. Explorative analysis on AQ-10 Positive participants without the diagnosis (i.e. 'false positives') showed significantly elevated autistic symptoms. The prevalence of autism in Hong Kong is comparable to the recent estimates in Western countries, which poses a significant public health challenge. Despite the high false-positive rates, AQ-10 remains valuable for excluding autism and identifying those with autistic symptoms. Furthermore, community-based studies are crucial to address sex differences in autism expression.