BACKGROUND: The medical profession is often presented with information on the value of treatment in terms of likely risk reduction. If this same information was presented to patients--so enabling them to give proper informed consent--would this affect their decision to be treated? AIM: To examine patients' choice about treatment in response to different forms of risk presentation. DESIGN OF STUDY: Postal questionnaire study. SETTING: The questionnaire was sent to 102 hypertensive patients and 207 matched non-hypertensive patients aged between 35 and 65 years in a UK general practice. METHODS: Patients were asked the likelihood, on a four-point scale, of their accepting treatment for a chronic condition (mild hypertension) on the basis of relative risk reduction, absolute risk reduction, number needed to treat, and personal probability of benefit. RESULTS: An 89% response rate was obtained. Of these, 92% would accept treatment using a relative risk reduction model, 75% would accept treatment using an absolute risk reduction model, 68% would accept treatment using a number needed to treat model, and 44% would accept treatment with a personal probability of benefit model. CONCLUSION: Many patients may prefer not to take treatment for mild hypertension if the risks were fully explained. However, given that the form of the explanation has a strong influence on the patient's decision, it is not clear how decision-making can be fully shared nor what should constitute informed consent to treatment in this situation.