Aim: To study the effect of onset age on clinical characters and progress of Parkinson disease. Methods: Sixty-six early-onset patients with Parkinson disease(≤ 50 years of age) and 173 later-onset patients(> 50 years of age) were selected from Xuanwu Hospital of Capital University of Medical Sciences from December 2000 and August 2004. The rate of sex, onset symptoms, family history, the duration reaching different Hoehn and Yahr stages and the use and response of L-dopa drug therapy between early-onset and later-onset patients were compared. Results: All 239 patients were involved in the result analysis. 1 The rate of male was 48% (32/66) and 56% (97/173) in early-onset and later-onset patients, and there was no significant difference in rate of sex between early-onset and later-onset patients(χ2 = 1.106, P = 0.293). 2 Static tremor was as onset symptom in later-onset patients(62.4%, 108/173); motor retardation was as onset symptom in early-onset patients(47%, 31/66); there was significant difference in onset symptom between the two groups(χ2 = 4.849, P = 0.028). 3 The rate of positive family history in the early-onset patients(11%, 7/66) was higher than that of later-onset cases(4.0%, 7/173) (χ2 = 3.728, P = 0.054). The rate of combining cases of positive and possible family history in early-onset patients(20%, 13/66) was higher as compared with that in later-onset cases(8.7%, 15/173) (χ2 = 5.616, P = 0.018). 4 Although the difference in time between onset of disease and reaching to different Hoehn and Yahr stages was not significant between the early-onset group[(4.3 ± 3.4) years] and the later-onset patients[(2.8 ± 2.2) years], the time interval reaching Hoehn and Yahr stage 2-2.5 and over 3 in early-onset group[(6.6 ± 5.4), (8.9 ± 4.0) years] was significantly longer as compared with that in later-onset patients[(8.9 ± 4.0, (5.6 ± 3.6) years], respectively(t = 2.380, 2.362; P = 0.023, 0.023). 5 There was no significant difference in same dose of L-dopa at same Hoehn and Yahr stage [1-1.5 stage: (397.5 ± 217.5) mg vs(437.2 ± 233.1) mg] (t = -0.491, P = 0.626); 2-2.5 stage: (541.3 ± 299.9) mg vs(487.6 ± 237.0) mg (t = 0.822, P = 0.414); above 3 stage: (517.1 ± 285.3) mg vs (573.3 ± 301.7) mg(t = -0.470, P = 0.641). The time starting to use L-dopa therapy in early-onset patients[(41.2 ± 46.8) months] was much later than that in later-onset patients[(24.7 ± 22.7) months]. Conclusion: The onset age and onset symptom relate to the progress of Parkinson disease. does affect Parkinson disease clinical characteristics, the mode of progression, and response to L-dopa treatment, supporting the heterogeneity of PD. Genetics may play a more important role in the early-onset patients. Though the early-onset patients start late to use L-dopa treatment, the onset age do not affect the dose and effect of L-dopa significantly.