The RAS/mitogen activated protein kinase (MAPK) pathway is implicated in growth-factor mediated cell proliferation, differentiation and cell death Recent studies have revealed dysregulation of the RAS/MAPK cascade to be the common molecular basis for congenital multiple anomaly/mental retardation syndromes: Noonan syndrome, LEOPARD syndrome, Costello syndrome and CFC syndrome. Neurofibromatosis type I , which is caused by loss-of-function mutations of NF1, can also be included in the same disease entity, while patients with NF1 are not usually associated with facial dysmorphisms or cardiac anomaly. We suggest that †Noonan syndrome, LEOPARD syndrome, Costello syndrome, CFC syndrome, and neurofibromatosis type I may be comprehensively termed the RAS/MAPK syndromes.