Myelinogenesis is a scheduled process that depends on both the intrinsic properties of the cell and extracellular signals. In rat brain, myelin development is an essentially postnatal event and environmental interferences could affect myelin synthesis. Nutrition plays an important role, since severe postnatal malnutrition and essential fatty acid (EFA) deficiency cause hypomyelination. Even though the dietary effects are more pronounced in the postnatal period, dietary lipids can affects myelin development also in the postweaning period. Rats fed with diets rich in polyunsaturated n3 fatty acids showed a decrease of the relative amount of myelin basic protein (MBP) and a CNPase activity indicating a delay in myelin deposition and/or an instability of its structure. Our recent studies have shown that dietary fatty acids can be positively involved in the control of central nervous system (CNS) myelinogenesis. Offspring of rats fed diets containing odd chain fatty acid during pregnancy and lactation show an early development of behavioral reflexes linked to myelination compared to controls fed a diet containing margarine. Subsequent studies have shown that the expression of myelin proteins is higher in test than in control animals, but the mechanism of the action of fatty acids is still unknown. Also human brain myelinogenesis can be affected by environmental factors. EFA deficiency has been well studied for the important role of C22:6 (a C18:3 metabolite) in the vision system development. The observation that dietary fatty acids can affect membrane composition has led to the use of modified diets in some CNS pathological conditions. For example, preterm infants characterized by low levels of C22:6 and fed with formulae diets enriched in this fatty acid, show a recovery of visual function. The administration of C22:6 has also been tested in patients affected by peroxisomal biogenesis disorders which are associated with very low levels of this fatty acid in the brain. During the treatment, C22:6 content increases in red blood cells, and probably in the brain membranes, as considerable neurologic and electrophysiological improvement suggest. A mixture of glyceryltrierucate and glyceryltrioleate has been tested in the demyelinating disease Adrenoleukodistrophy which is characterized by an abnormal accumulation of very long chain fatty acids (VLCFA) in tissues and fluids. The diet is able to lower VLCFA levels in plasma, but its efficacy for myelin damage is debated. Lastly, a diet which reduces the intake of saturated fatty acid and increases the quantity of polyunsaturates is suggested for multiple sclerosis patients since a decrease of linoleic acid in their plasma and erythrocytes has been observed. Such a diet seems able to reduce the severity of the attacks.