Several key signalling pathways, such as Hedgehog, Notch, Wnt and BMP-TGFbeta-Activin (bone morphogenetic protein-transforming growth factor-beta-Activin), are involved in most processes essential to the proper development of an embryo. It is also becoming increasingly clear that these pathways can have a crucial role in tumorigenesis when reactivated in adult tissues through sporadic mutations or other mechanisms. We will focus here on the Hedgehog pathway, which is abnormally activated in most basal cell carcinomas, and discuss potential therapeutic opportunities offered by the progress made in understanding this signalling pathway.