It has been confirmed in research that immune system plays an important role in the development of some tumors, for example skin tumors. Different immune factors, such as NK cells, T cells, various interleukins and interferon-gamma (IFN-gamma), have a significant influence on the process of tumor development and appearance of metastasis. On the other hand, many studies have confirmed the influence of psychological factors on different aspects of the immune system, including the immune cells important in the process of tumor development, and it is supposed that psychological factors in this way subsequently influence tumour development. It is assumed that endocrine system also has important role in process of growth and development of skin tumor. Some studies indicate the importance of cortisol, ACTH, and female sex hormones in the occurrence of skin tumors, especially malignant melanoma. It has been confirmed in research that there is a significant influence of psychological factors on the secretion of some hormones, mainly cortisol. Finally, some studies have shown that psychological distress may have an impact on two important aspects of carcinogenesis: repair of damaged cellular DNA and apoptosis. Many carcinogens stimulate tumor development just through destruction of cell DNA, which leads to an increased number of abnormal cells, therefore DNA repair acts as one of the key mechanisms in the fight against carcinogens. Apoptosis as a process of autodestruction of damaged cells also represents an important mechanism of antitumor actions. Correlation studies have given important contributions to the confirmation of connections between the psychological, immune and endocrine factors in tumor development, but intervention studies can give a more detailed insight into these connections. Although it was supposed that psychological factors could influence the process of tumor development, only lately, with improvement in the area of psychoneuroimmunology, new methods and study designs have appeared that allow for examination of the process underlying this influence.