Activating oncogenic mutations of the RAS gene are common in cancer, occurring in 30% of solid tumours in adults. Inhibitors of the enzyme farnesyl protein transferase prevent a key step in the post-translational processing of the RAS protein, and were developed initially as a therapeutic strategy to inhibit cell signalling in RAS-transformed cells. As more has been learnt about the biological effects of farnesyl transferase inhibitors on cancer cells, it has become increasingly clear that tumours without oncogenic RAS mutations may also be targets for farnesyl transferase inhibitor therapy. Encouraging results from phase I and II clinical trials have emerged, creating both enthusiasm and new challenges for the optimum clinical development of this important new class of anticancer drug.