L-Carnitine was proposed as a potential treatment for patients diagnosed with autism to ameliorate the behavioral symptoms associated with the disease. 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 showed significant improvement in CARS scores (P-groups less than 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 greater than 0.5, P greater than 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. (Contains 9 tables.)