A survey by multiple choice questionnaire of 40 doctors, 60 health support staff and 120 patients investigated the understanding of common medical and psychological terms. Significant differences in levels of understanding were found between these groups, and level of medical education predicted the level of correct understanding. The widest gap in doctor-patient understanding was shown for common psychological terms. These terms constitute a major part of doctor-patient interactions and such differences could cause difficulty in effective doctor-patient communication.