Carnitine is essential for the lipid and carbohydrate metabolism, and proper metabolic control in type 1 diabetes has potential impact on long-term complications. The plasma total, free, and acylcarnitine levels in 47 children and adolescents with type 1 diabetes were determined by a radioisotopic assay and compared to the values of a series of anthropometric measurements and metabolic parameters, including blood glycosylated hemoglobin Alc, serum cholesterol and triglycerides, and urine microalbumin levels. Plasma values for total, free, and acylcarnitine were 30.1+/-7.26, 20.0+/-4.50, and 10.2+/-6.47 micromol/l, respectively. Acyl/free carnitine ratio was 0.544+/-0.369. Individuals with type 1 diabetes had significantly lower total and free carnitine levels and significantly higher acyl/free carnitine ratios than controls (P<.001). Plasma total and free carnitine levels were inversely correlated to the duration of diabetes (P=.036 and P=.071, respectively). No statistical relationship was documented between carnitine levels and the remaining anthropometric and metabolic variables. In conclusion, total and free carnitine levels are decreased in children and adolescents with type 1 diabetes. This reduction is time related and may have potential interactions with the long-term complications of type 1 diabetes. Larger studies are required for final conclusions to be drawn on the precise role of carnitine and the possible benefit, if any, of carnitine supplementation in diabetic patients.