Abstract Awareness of autism spectrum disorder (ASD) within public and medical domains has increased. Demand on services is high as children and young people are being presented for earlier advice, assessment and diagnosis. To maximise detection and minimise harm it is essential for all clinicians working with children including primary care teams, allied healthcare professionals, educational and social care staff to have a sound knowledge of the presentation and assessment of autism spectrum disorders (ASD) and an understanding of the co-morbidities. Whilst routes of entry for referrals can vary due to a diversity of presentation and local service provision, there are standards in the recognition, referral and diagnosis of autism. Early identification is advantageous in order to maximize the child's potential, provide appropriate support and targeted intervention for ASD and co-occurring conditions with the aim of improving outcomes. This review addresses the diagnosis of ASD and provides an assessment framework for professionals who encounter a child with a suspected autism spectrum disorder.