Based on scientific findings of the last several decades omega 3 fatty acids contained mainly in fish, especially their long-chain polyunsaturated representatives (LC-PUFA) EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), are considered essential for the physical and mental development of children. A lack of these essential fatty acids is linked to various clinical pictures in children such as dyspraxia, dyslexia, dyscalculia or infantile depression. On the other hand, a growing number of findings verify that EPA and DHA not only relieve impairments associated with developmental disorders, but also have beneficial effects on the cognitive performance of psychologically healthy children in preschool and school-age. Based on these findings, the presented pilot study examined the cognitive level of development (measured with the WET - Wiener Entwicklungstest) of three to six year old children (M = 5.3 years, SD = 0.7) before and after eight weeks of supplementation, with respect to the four components working memory, verbally expressed knowledge as well as spartial and logical-inductive reasoning. The 41 children of the treatment group were on the daily intake of a high-dose fish oil preparation (740-825 mg EPA; 460-550 mg DHA) significantly improved from the first to the second time of measurement in all of these four areas, whereas in the 35 children belonging to the waiting group without dietary supplements in the same period, no increase of mental performance was observable. The results found suggest a possible positive effect of increased omega-3 fatty acid consumption on the cognitive development of healthy preschoolers.