Epidemiological literature suggests a protective effect of omega-3 (n-3) polyunsaturated fatty acids (PUFAs) against cancer. They are attributed to have significant anti-inflammatory properties, and are reported to directly inhibit carcinogenesis and tumor expansion, whilst also reducing the risk for secondary complications, thus representing a promising approach for adjunctive chemotherapy treatment. At the same time, the incidence of malnutrition amongst children with cancer is high and both under- and overnutrition are associated with detrimental consequences, including increased risks for morbidity and mortality, early relapse rates, and a higher prevalence of secondary complications during treatment. Taken together with the benefits of n-3 PUFA supplementation, an enhancement of the nutritional status is a potentially modifiable prognostic factor in pediatric oncology.