The present invention provides for methods and compositions for treating medium chain acyl-CoA dehydrogenase deficiency. It is based, at least in part, on the discovery that phenylbutyrate can serve as a substrate for medium chain acyl-CoA dehydrogenase. In non-limiting embodiments, phenylbutyrate and/or another source of phenylacetate is administered as a chaperone treatment to patients suffering from medium chain acyl-CoA dehydrogenase deficiency.
