PTSD is the only anxiety disorder with a known cause, which develops after exposure to a traumatic event, however, all persons exposed to trauma do not develop PTSD. The main aim of this study was to identify groups of patients according to specific initial psychological and clinical characteristics which make these patients more likely to achieve significant progress in the recovery process. Secondary aim of the study was the first evaluation of differences in effectiveness between homogeneous and heterogeneous groups regarding their clinical picture. The sample consisted of 86 veterans suffering from chronic PTSD who were consecutively admitted to Regional Centre for Psychotrauma in Split and Psychiatric Hospital 'Sveti Ivan' in Zagreb. The following measures have been used: The COPE Inventory, The Crown-Crisp Experiential Index (CCEI), The Mississippi Scale for Combat-Related PTSD (M-PTSD), Beck Depression Inventory (BDI-II), The Quality of Life Scale. The results have shown that it is possible to predict a decrease in the PTSD symptoms on the basis of data about enduring personality change after catastrophic events, while a reduction of depressive symptoms can be predicted on the basis of indicators of hysterical personality. Furthermore, it is also possible to predict the improvement in the quality of life after the therapy based on the number of previous hospitalisations and somatic manifestations of anxiety. Homogeneous groups have turned out to be more effective compared to heterogeneous ones in treating depression. The study has shown that predictors of a positive outcome of psychodynamic group therapy on veterans suffering from chronic PTSD are the following: enduring personality change after catastrophic events, age, work status, the number of previous hospitalisations, somatic manifestations of anxiety and hysterical personality.