In diabetes mellitus (DM), increased fatty acids have negative effects on pancreatic beta-cell functions, in addition to enhanced mitochondrial transportation of fatty acids related to decreased insulin levels. The aim of this study was to evaluate lipid metabolism in children with DM by measuring plasma fatty acids and carnitine fractions to reveal relationships between carnitine status and increased fatty acid oxidation. Increased plasma fatty acids (except for arachidonic acid, there were no significant differences in the ratio of each specific fatty acid to total fatty acids), lipoprotein (a), acyl carnitine levels and urinary total and free acyl carnitine excretion, and decreased plasma free carnitine levels, were found in children with DM. There were no correlations between the duration of DM or HbA1c and study parameters. It is recommended that plasma free carnitine determinations should be made even if the patient has good metabolic control.