Investigators who conduct clinical pain research are required to obtain voluntary informed consent from patients. However, little is known about what information patients expect when they decide whether to enroll in such studies. It is important that investigators understand these information needs so they can effectively and clearly describe the research risks and potential benefits that matter to potential subjects. By understanding these needs for information, investigators may also be better able to anticipate patients' concerns and to recruit subjects more efficiently. This study was designed to define information needs that patients have when they decide whether to participate in clinical pain research. This paper describes these information needs, and identifies clinical and demographic variables associated with specific needs.