The use of a cochlear implant (CI) to restore some acoustical input to patients with complete acquired hearing loss may be expected to result in changes in their psychological functioning. CI programmes should therefore include a careful psychological screening of all candidates and subsequent psychological assessments of patients who receive implants. Procedures used in the psychological assessment of CI candidates and patients outlined in the literature, as well as those used in the Royal Ear Hospital (REH) programme, are discussed. It is concluded that standard psychological tests of personality and intellectual functioning are of limited value in the screening of CI candidates and the postoperative evaluation of patients. It is proposed that more useful information be obtained by an analysis of the possible functional value of the implant to each individual candidate and by assessment of actual postoperative changes in the patient's behaviour. Unless an implant leads to improvements in the patient's psychosocial functioning, the device is unlikely to be used. Examples of this approach in assessing the REH candidates and patients are given.