Noonan syndrome is a common autosomal dominant condition, readily recognisable in childhood. It is characterised by a pattern of typical facial dysmorphism and malformations including congenital cardiac defects, short stature, abnormal chest shape, broad or webbed neck, and a variable learning disability. Mildly affected adults may not be diagnosed until the birth of a more obviously affected child. The phenotype is highly variable. Important progress in understanding the molecular basis of this and other related conditions was made in 2001 when germline mutations in the PTPN11 gene were found to account for ∼50% of cases. Since then, mutations in additional genes in the rat sarcoma (RAS) pathway have been identified in a proportion of the remainder. Molecular confirmation of diagnosis is now possible for many families and has become increasingly important in guiding management. Increased awareness by paediatricians will lead to earlier diagnosis, and provide patients and their families with accurate genetic counselling, including options when planning pregnancy.