Objective: To observe the relation between onset age and the motor complications involved Parkinson's disease (PD). Methods: The detailed clinical information of 195 patients with idiopathic PD and good response to L-dopa were recorded and followed up. The data were calculated with SPSS statistic software. Results: Although the time interval between the onset of the disease and the use of L-dopa was significantly longer in the 57 early-onset patients as compared to the 138 later-onset ones ((3.88 ± 3.33) years vs (2.36 ± 2.21) years, t = 3.142, P = 0.002), the time interval between the use of L-dopa and the occurrence of motor complications was not significantly longer in the early-onset group ((3.81 ± 2.06) years vs (4.24 ± 2.00) years, t = -0.888, P = 0.378). There was no difference in the constituent ratio of non-L-dopa use from onset between early-onset and later-onset PD groups (28.07% (16/57) vs 27.54% (38/138), x 2 = 0.006, P = 0.940). There was also no difference in the dosage of daily L-dopa use when motor complications occurred between early-onset and later-onset PD groups ((601.8 ± 296.7) mg vs (655.6 ± 192.5) mg, t = -0.912, P = 0.365). Seven-tenths of the patients with an onset age younger than 40 years old carried the risk of motor complications after using L-dopa for 5-years and those older than 70 years had the risk at a rate of 1/10. Conclusions: Delaying the of use of L-dopa may not necessarily delay the onset of motor complications. The high incidence of motor complications among younger patients may not be related with drug dosage and the type of drug firstly chosen. Younger onset age does increase the incidence of motor complications. © 2009 by the Chinese Medical Association.