The age at which autism can be diagnosed has been pushed earlier over the past decades. There is a strong narrative among clinicians and some parent groups that ‘earlier is better’ for diagnosis, detection and intervention, before a crucial period of brain plasticity has passed. Others argue that the evidence for stability of diagnosis and development trajectory is limited in younger children. This chapter reviews the evidence for early detection and intervention for babies and children ‘at risk’ of developing autism, covering ‘baby-sibs’ studies, biomarkers and neuro-markers. It also considers the effect of the early detection narrative in casting autism as a tragic occurrence and the ramifications for parents, particularly mothers, and autistic people themselves. Surveillance medicine and early childhood monitoring, to report proto-autism behaviours, surely lead to more early referrals and ultimately more diagnoses, contributing, perhaps in a small way, to autism’s rise.