Four studies in which a patient self-disclosure questionnaire was developed and tested are reported. The instrument was designed to include only content judged by both patients and clinicians as important. Three areas of patient difficulty in disclosing to a health care provider were measured: personal problems and feelings, responses to health care, and life style. Patient difficulty in disclosure was assessed by 21 7-point rating scales, 7 for each disclosure area; ratings were summed to obtain scores. A correlation matrix of the ratings of 216 patients was subjected to a three-factor principal components analysis with varimax rotation; the solution accounted for 59% of the total variance. High internal consistency and test re-test reliability for the total scale and subscales were obtained; Cronbach's alpha .82-.83, n = 214; r = .81-.87, n = 66. In separate tests of construct validity patient self-disclosure was shown to be influenced by locus of control and perception of clinician empathy, and to covary with heart rate changes.