Brain white matter myelin abnormalities and cell membrane fatty acid abnormalities have been implicated in schizophrenia and other psychiatric disorders. We investigated in young adults with a psychotic disorder (n=12) whether (poly)unsaturated fatty acid concentrations in erythrocyte membranes are related to an MRI measure of brain white matter, which depends on the degree of myelination. A significant correlation was found between total (poly)unsaturated fatty acid concentration and fractional anisotropy of a fronto-temporal white matter tract (r=0.503, P=0.048). Unsaturated fatty acids may be necessary for the myelinating activity of oligodendrocytes or for myelin maintenance. These results warrant further investigation.