Most patients who experience illness symptoms develop an explanatory model. More frequently than physicians realize, these attributions involve serious and potentially life-threatening medical conditions. Only a minority of patients spontaneously disclose or "offer" their ideas, concerns, and expectations. Often patients suggest or imply their ideas through "clues." Active listening is a skill for recognizing and exploring patients' clues. Without this communication skill, patients' real concerns often go unrecognized by health care professionals. Qualitative techniques including videotape analysis, postinterviewing debriefing, and interpersonal process recall were used to identify types of clues. We propose a taxonomy of clues that includes (1) expression of feelings (especially concern or worry), (2) attempts to understand or explain symptoms, (3) speech clues that underscore particular concerns of the patient, (4) personal stories that link the patient with medical conditions or risks, and (5) behaviors suggestive of unresolved concerns or unmet expectations. This clue taxonomy will help physicians recognize patients' clues more readily and thereby improve their active listening skills. A deeper understanding of the true reasons for the visit should result in increased patient satisfaction and improved outcomes.