This report is one of several reports focusing on the role of omega-3 fatty acids (FA) in the prevention or treatment of various diseases. This report focuses on the effects of omega-3 FA on cognitive function with aging, dementia, and neurological diseases. Over the past 40 years, an increasing number of physiological functions have been attributed to omega-3 FA, including movement of calcium and other substances into and out of cells; relaxation and contraction of muscles; regulation of clotting and of secretion of substances that include digestive enzymes and hormones; and control of fertility, cell division, and growth. In addition, omega-3 FA may play an important role in brain development and function. Docosahexaneoic acid (DHA; 22:6n-3) is the precursor to a newlydescribed metabolite called 10,17S-docosatriene, which is part of a family of compounds called resolvins. They are released in the brain in response to an ischemic insult and counteract the pro-inflammatory actions of infiltrating leukocytes by blocking interleukin 1-beta-induced NF-kappaB activation and cyclooxygenase-2 expression. DHA also plays a role in retinal rod outer segments by influencing membrane fluidity so as to optimize G protein coupled signaling. The major dietary sources of omega-3 FA in the U.S. population are fish, fish oil, vegetable oils (principally canola and soybean), walnuts, wheat germ, and some dietary supplements. THe following questions are addressed in this study: 1. What is the evidence that omega-3 FA play a role in maintaining cognitive function in normal aging? 2. What is the evidence that omega-3 FA affect the incidence of dementia including Alzheimer's disease? 3. What is the evidence that omega-3 FA are effective in the treatment of dementia including Alzheimer's disease? 4. What is the evidence that omega-3 FA affect the incidence of neurological diseases? 5. What is the evidence that omega-3 FA prevent the progression of multiple sclerosis?