Since 1968, we have had the opportunity to handle several hundreds of patients suffering from Parkinson’s disease with L-dopa associated with decarboxylase inhibitor. This study reports the results obtained in 304 patients. It demonstrates the efficiency of the treatment, and also stresses its possible side effects and the difficulties to conduct such a treatment. These difficulties may only be avoided by using extreme carefulness, and by a thorough follow-up of patients. This work also shows the absence of liver toxicity of the drug used.