Angiotensin converting enzyme inhibitors (ACEi) prescribed for cardiovascular and renal disease since 1980 are widely atoxic and several experimental studies and one epidemiological study have demonstrated an effect of ACEi on cancer. ACEi has the effect of modifying gene expression; inhibiting proliferation and invasion of cancer cells; reducing endothelial cell migration and angiogenesis in vitro, whereas tumour growth and metastasis were inhibited in vivo. Several mechanisms of action are possible but inhibition of matrix metalloprotease activity, reduced expression of vascular endothelial growth factor and interference with the renin-angiotensin system were demonstrated by the experimental studies. In this paper we review the laboratory investigations and epidemiological studies on the anti-cancer actions of ACEi and present a summary of the evidence regarding the potential use of ACEi in cancer treatment.