We have analysed the side effects of levodopa preparations in patients suffering from Parkinson's disease. The study has begun in 1993. All the patients were initially admitted in the Neurological Clinic of the Recovery Hospital in Iasi, and then followed in ambulatory condition. We have monitorized the apparition of adverse reactions of levodopa therapy, and tried to treat them by modifying doses and patterns of administration, by associating other drugs or by replacing levodopa with other drugs. We have initially included 116 patients, of whom 30 have developed secondary effects until June 2002. The most frequent secondary effects have been coreea, dystonia, mental adverse reactions, yo-yo-ing etc. Each one of the 30 patients has developed one or more types of secondary reaction.