Transplant candidates completed the Every Day Problems test (EPT), a performance-based measure of instrumental activities of daily living (IADL), and the Katz self-report scale of IADL functioning. Caregivers estimated the candidate's IADL capacity using the Katz scale. A healthy community group and patients with cardiac disease not undergoing transplant evaluation and their caregivers served as controls. Discrepancies between the EPT and Katz scales were generated. Results showed that the total number of discrepancies was significantly higher among the two patient groups as compared to controls. Three or more discrepancies (a total of 7 IADL domains were assessed) occurred in 40-52% of the participants and their caregivers in the two patient groups. Similarly, the total number of discrepancies between the Katz scale of the participant and their caregiver was significantly higher among the two patient groups as compared to controls, with only 33-44% showing perfect agreement in the patient groups as compared to 97% among controls. Despite a high prevalence of discrepancies in both patient groups, results did not support the hypothesis that transplant candidates tend systematically to overestimate their ability level on self-report IADL measures. © 2000 Plenum Publishing Corporation.