The targeting of the ATP binding pocket of the epidermal growth factor receptor (EGFR) tyrosine kinase, by the small molecule drugs gefitinib and erlotinib, represents a promising new therapeutic strategy in non-small cell lung cancer. However, it is now apparent that only a subset of patients responds to such treatment. Two publications in early 2004 reported the presence of activating mutations in the EGFR tyrosine kinase gene conferring exquisite sensitivity to these drugs. Several publications have since reported prospective data consistent with this finding. This brief review summarises the mutation data from 15 such studies in terms of mutation frequency by clinicopathological features and correlation with response to tyrosine kinase inhibition. A new paradigm for the routine detection of such mutations is needed to facilitate patient selection for treatment and further studies.