Cancer patients are at risk of developing malnutrition from underlying disease as well as from cancer treatment. Moreover, weight loss is considered as a predictive factor for disease progression and shorter survival time. As many as 10–20% of patients with cancer die from the results of malnutrition, instead of from the cancer itself. In the case of cancer-related malnutrition, it is necessary to quickly implement individualized nutritional support depending on the type and stage of the disease, metabolic changes, the patient’s condition, expected survival and the function of the gastrointestinal tract. Artificial nutrition reduces the side effects of chemotherapy and improves immunity. Perioperatively it reduces the risk of infection, facilitates wound healing and shortens the length of hospitalization, thereby reducing the costs of the treat- ment. Initially, a malnourished patient, without gastrointestinal dysfunction, qualifies for nutritional counseling. When the energy needs cannot be met by normal feeding, nutritional supplements, taken orally, are recommended. The next step is to feed the patient by nasogastric tube or percutaneous endoscopic gastrostomy. Parenteral nutrition, which results in more side effects, is only started when enteral nutrition is insufficient to ensure adequate nutritional status or in cases of gastrointestinal tract obstruction. The benefit of parenteral nutrition is that it especially provides for those patients with gynaecological cancer who have radiation-induced intestinal damage and post-surgical complications such as short bowel syndrome. Palliative nutrition must to relieve hunger and thirst. Nutritional interventions should be individualized and focused on the changing nutrient needs of the patient and should be supported by physical activity. Regular assessment of the nutritional status of the patient should be an inherent element of the oncological treatment.