Antihypertensive treatment may promote cancer through unknown mechanisms. Early retrospective studies implicated reserpine in breast cancer, but the drug was later absolved by prospective analyses. Data from case-controlled studies and several cohort studies suggested an association between the use of a diuretic and the occurrence of renal cell cancer. Several prospective studies showed that treatment with atenolol may increase mortality from malignancy. However, other studies that analyzed data from several thousand patients could not confirm this association. In two prospective studies, angiotensin-converting enzyme (ACE) inhibitors were associated with increased mortality from malignancy, but a few case-controlled studies showed no association between use of ACE inhibitors and malignancy. In addition, a recent retrospective study showed that long-term use of ACE inhibitors had a protective effect against malignancy. In some studies, calcium antagonists were implicated in increasing the risk for cancer; however, two large case-controlled studies and the combined data from nine observational studies showed a similar risk for malignancy among users and nonusers of a calcium antagonist. Ongoing long-term prospective studies will tell us more about the carcinogenicity of cardiovascular drugs.