In recent years, the pleiotropic effect of vitamin D in the human body has been emphasized more and more often. The results of research on the impact of vitamin D on the immune system and neoplasm prevention are extremely interesting. In this aspect, the role of omega-3 fatty acids is also considered. In this study, the authors attempted to systematize the current knowledge on these issues. However, it should be stressed that, in order to determine the role of vitamin D and omega-3 fatty acids in the prevention of the development of individual neoplasms, it is necessary to conduct further multicentre, randomized studies of a prospective nature because the results, so far, are inconclusive.