l-carnitine is present in mammalian cells as free carnitine and acylcarnitines. The acylcarnitine profile has been shown to be useful in identifying inborn errors of metabolism and to be altered under different metabolic conditions. While carnitine's most widely known function is its involvement in beta-oxidation of fatty acids, it may also have other roles in metabolism. The importance of acylcarnitines in tissues with high rates of beta-oxidation such as heart and muscle is intuitive. However, acylcarnitine and carnitine supplementation have resulted in beneficial effects in the treatment of various neurological diseases, even though fat is not the major fuel for brain. Recent data indicate new, multifactorial roles for acylcarnitines in neuroprotection. Brain acylcarnitines can function in synthesizing lipids, altering and stabilizing membrane composition, modulating genes and proteins, improving mitochondrial function, increasing antioxidant activity, and enhancing cholinergic neurotransmission. Currently a relatively small subset of acylcarnitines is usually investigated. More research is needed on the use of acylcarnitines in the treatment of neurological diseases using a list of acylcarnitines encompassing a wide range of these molecules. In summary, carnitine is not merely a cofactor in beta-oxidation, but rather it has many known and yet to be discovered functions in physiology.