OBJECTIVES: 1) To Study the effect of L-carnitine supplementation on behavioral symptoms in autistic children; 2) Study the effect of l-Carnitine supplementation on Acyl-Carnitine profile of Autistic children; 3) Detect possible correlation between the blood Carnitine status and Autistic behavior; and 4) Tolerability assessment of l-carnitine supplementation.  METHODS: Thirty children diagnosed with autism were randomly assigned to receive (100 mg/kg bodyweight /day) of liquid l-carnitine (n=16) or placebo (n= 14) for 6 months. Measurements included changes in childhood autism rating scale (CARS) form and free and total carnitine levels using tandem mass spectrometry. RESULTS: Results showed significant improvement in CARS scores (P-groups <0.001) and (P –overtime= 0.006), with statistically significant differences in free carnitine levels (P=0.027) and total carnitine levels (P=0.036 ) . There was no correlation between baseline free and total carnitine levels with changes in CARS scores from zero to 6 months (r > 0.5 , P>0.05) and generally L-carnitine therapy was well tolerated. In conclusion,   L-carnitine therapy (100 mg/kg -bodyweight/day) administered for 6 months significantly improved the autism severity, but subsequent studies are recommended.  CONCLUSIONS: 1) Significant differences were found in free and total carnitine levels after therapy; 2) Clinically, L-carnitine supplementation improves autism severity; 3) L-carnitine therapy was well tolerated; and 4) L-carnitine supplements may be given as part of autism treatment regimen.