In the course of cancer disease, many oncological patients develop tumor-associated malnutrition characterized by an insufficient supply of macro- and micronutrients. The inadequate nutritional status and the cancer anorexia-cachexia syndrome related to it are clinically relevant, as the response to antineoplastic measures, such as radiation and chemotherapy, is diminished, their side effects aggravated and the patient's quality of life and prognosis negatively affected. Therefore, the supportive nutrition care of oncological patients is of central importance. In this context, vitamins, minerals and long-chain omega -3 fatty acids are becoming more and more relevant in oncology although the benefit of such supplements is discussed controversially. Starting from a description of the etiopathogenesis and the pathophysiological consequences of cancer-associated malnutrition, the present study provides an overview of the importance of micronutrients for oncological patients. In the case of reduced food intake and/or inappropriate food choice the use of a multi-vitamin-multimineral supplement administered in physiological doses, i.e. nutrient quantities approximately corresponding to the recommended daily allowances, can be generally recommended. However, to enhance postoperative wound healing, it seems that cancer patients require higher amounts of micronutrients than healthy individuals. Because vitamin D deficiency is highly prevalent in oncological patients, improvement of vitamin D status is of special interest.