Hypertension is often poorly controlled despite its importance and despite the availability of very effective treatments. Many factors contribute to poor control, including failure of patients to attend physicians, failure of physicians to detect and adequately treat hypertension to goal levels, and failure of patients to persist with prescribed therapy. An under-recognized problem is the failure, both in writing and in the application by third party payers, of consensus guidelines to recognize the important difference between efficacy in clinical trials and effectiveness in clinical practice. The issue of applicability of guidelines to actual practice was studied in the context of a Canadian Family Medicine teaching practice. At the time of the study, consensus guidelines for management of hypertension recommended that drug therapy be initiated with a beta-blocker or diuretic, except for patients with complicated hypertension for whom these drug classes are relatively contraindicated. It was generally assumed that widespread use of other classes of drugs represented inappropriate and wasteful use of resources. By a retrospective chart audit, we determined the proportion of patients in a family practice for whom therapy with a beta-blocker or diuretic was contraindicated, and examined the compliance of the physicians in the practice with guidelines. We found that about half of hypertensives had conditions for which recommended therapy is not a beta-blocker or diuretic. Thus, failure of physicians to follow guidelines is apparently less inappropriate than is widely perceived.