Introduction: The etiopathogenesis of psoriasis and psoriatic arthritis is not entirely acknowledged. It is assumed that the development of psoriasis and psoriatic arthritis is influenced by interaction of genetic and environmental factors. According to the new data psoriasis is classified as a psychosomatic skin disease. Psychosocial factors in combination with genetic background play a key role in the development of psoriasis and psoriatic arthritis. For their treatment it is neccessary to use an interdisciplinary approach. The aim of the research was to explore both positive and negative life experiences, different stress situations that happened before the appearance of psoriasis and psoriatic arthritis, defense mechanisms and types of aggression in patients with psoriasis and psoriatic arthritis. It has also been investigated their possible correlation with the disease severity. Patients and methods: The study includes 100 psoriatic patients and 45 psoriatic patients with psoriatic arthritis. The control group consisted of 101 patients that suffered from dermatosis which had no influence on their psychological and physical wellbeing. All participants were asked to fill out a questionnaire with sociodemografic data and several psychological questionnaires: a trauma antecedent questionnaire, a life experience scale, a life style questionnaire and a questionnaire for the evaluation of aggression. In all psoriatic patients the severity of psoriasis has been estimated according to the Psoriasis Area and Severity Index (PASI scale). Results: Patients with psoriasis and psoriatic arthritis were exposed more frequently to multiple negative life experiences with the lack of positive life experience, especially during school (p=0.02) and adolescent age (p=0.01). Patients with psoriasis showed more frequently indirect or transposed aggression (p=0.026), verbal latent aggression (p=0.018) and total aggression (p=0.039). Patients with psoriasis and psoriatic arthritis do not experience more intense stress before the beginning of the disease, but they are more upset than the controls (p=0.0001). Patients with psoriatic arthritis significantly often use negation (p=0.005), projection (p=0.025) and intellectualization (p=0.0001) while psoriatic patients with these defense mechanism more often use reactive formation (p=0.0051) and regression (p=0.029) in comparison to the control group. The severity of psoriasis is in significant correlation with the defense mechanism of transponding. The transposition significantly correlates with all forms of aggression and is an important predictor of the severity of the clinical picture of psoriasis (Beta =0.366; p= 0.007). Conclusions: The study results of the association of positive and negative life experience, stress, aggression and defense mechanisms in psoriatic patients and patients with psoriatic arthritis show the important role of psychosocial factors in the multifactor etiopathogenesis of these diseases. Thus for the treatment of these patients interdisciplinary approach is needed which includes the participation of a dermatologist and a psychiatrist-psychotherapist.