Some parents experience concerns relating to their child's development and seek clinical assessments for their child's behaviour. We sought to understand the concerns that led parents to seek a general clinical assessment where some children were diagnosed with autism spectrum disorder. We conducted a systematic review to identify the types of parent concerns that drives parents to seek professional help for their child's development. Database searching identified 7587 records, where 10 studies (9 cohorts) met our inclusion criteria. Parent reported concerns were categorised using the coding schemes of included studies described as autism spectrum disorder-specific (i.e. communication, social or stereotyped behaviour concerns) or non-autism spectrum disorder-specific concerns (i.e. behaviour/temperament, developmental, medical, sensory or motor concerns). The most reported parental concerns prior to an assessment were speech and language, social and behavioural. Concerns were also reported relating to parent understandings of an autism spectrum disorder diagnosis and the positive and negative implications surrounding the autism spectrum disorder diagnosis. Data were reported descriptively due to variations in study design and data analyses. Additional rigorous research on parent concerns prior to a diagnostic autism spectrum disorder assessment is required to capture what drives parents to seek professional help to support their child's development.