A structured survey of patients in three illness groups (acquired immune deficiency syndrome, multiple sclerosis and mental disorders) was undertaken to describe patients' perspectives on privacy, consent and the use of their health information for medical research. The survey was distributed by mail to subjects in the AIDS and MS groups and was completed in a clinic waiting room by people in the mental disorders group. Of the 478 patients approached for participation, 235 returned completed surveys (response rate 49.2 percent). Most subjects were concerned about privacy and they valued opportunities to provide consent for the use of their personal health information for research. Contextual factors, such as identification, type of illness and who was conducting the research, were important to individuals' preferences in granting consent. When health information was used specifically for research, the majority of subjects wanted to be asked for their consent unless anonymity was assured. Privacy and control over personal health information were important to patients in these groups. Patients prefer to be asked for research access to their health information.