A randomized controlled trial of an information and medical record booklet designed to improve patient understanding and participation in the management of hypertension was conducted in six inner London general practices. After one year there were no significant differences between the group who had received the booklets and the control group in mean systolic or diastolic blood pressure, but the study group scored significantly higher on knowledge about hypertension and its management. However, the difference between the two groups was small, possibly because both groups started with a high level of understanding about hypertension and its management. In addition, the mean diastolic blood pressure in the control group showed that the treatment provided was already satisfactory, and that there was little need for improvement. Nevertheless, the information booklet evaluated in this study provides health professionals with a highly acceptable method of informing the patient about hypertension and its management and could be used both in hospital and general practice.