The aim of this article is to outline the usefulness of such categories as deficit and defect during the process of psychotherapy in psychodynamic terms. Because there is no one common definition of these concepts, first the author analyses how they are used in clinical practice (we talk about e.g. cognitive or different emotional deficits, organic or post psychotic defects). Sometimes these phrases have very pessimistic connotation for the outcome of psychotherapy. The author refers to different psychoanalytical theories (e.g. H. Kohut, M. Balint, H. Deutsch, F. Pine) to show that these concepts have their origins in two sources. First is the accumulation of psychological and neuropsychological knowledge on the determinants of irreversible changes in the patient's personality, which are located in his/her brain functioning, early relationships or developmental environment. The second is the strong experience of countertransference inefficacy and limits of psychotherapy as the method of facilitating positive changes in the patient's life. Clinical illustrations are used to show therapeutic implications of the concepts of deficit and defect. The author focused on the necessity of distinction between deficit and dissociation, interpersonal nature of deficit and defect diagnosis and the possible determinants and consequences of premature diagnosis of deficit or defect.