Early development of levodopa-induced dyskinesias and response fluctuations in young-onset Parkinson's disease. We evaluated whether patients with young-onset Parkinson's disease (PD) (onset between 21 and 40 years) develop levodopa-induced dyskinesias and motor response fluctuations more frequently and earlier than patients with older-onset PD (onset after 40 years) by determining the period from levodopa introduction to development of dyskinesias or fluctuations in 25 young-onset (mean age at onset, 33.54 years) and in 25 matched older-onset PD patients (mean age at onset, 55.76 years). Young-onset PD patients had significantly higher frequency for both dyskinesias and fluctuations after both 3 and 5 years of levodopa. Young-onset PD patients also developed both levodopa-induced dyskinesias and fluctuations earlier than older-onset PD patients. We suggest that the introduction of levodopa therapy in patients with young onset PD should be postponed as long as possible. 