Background: Causes of Parkinson disease have not been mentioned clearly up to now yet. Theory of hereditary susceptibility is the main theory to explain Parkinson disease now. But there is no definite conclusion on which hereditary factors have relationship with it. Objective: To study the relationship between gene polymorphism caused by point mutation C to T on cDNA 609 basic group of reduced NAD(P) H: quinone oxidoreductase (NQO1) gene and hereditary susceptibility of Parkinson disease. Design: A non-randomized synchronized control research based on patient and healthy people. Setting: Neurology departments in two university hospitals and a senile disease research institute in a university hospital. Participants: Totally 126 patients (Parkinson disease group) diagnosed as Parkinson disease in Neurology Clinic of First Hospital Affiliated to Sun Yat-sen University from September 1994 to September 1997, aged 46 to 73 years, in which 74 were males and 52 were females. Totally 136 healthy adults (control group), in which 66 were males and 70 were females, who came to the clinic to do health examination at the same time, aged 40 to 72 years. Methods: Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to analyze NQO1 gene polymorphism in Parkinson disease group and healthy adult control group. Main outcome measures: Mutation frequency and genotype of point mutation of basic group C to T on NQO1 gene cDNA 609 . Results: T allele frequency in Parkinson disease group was 52% and that in control group was 43%. There was significant difference between two groups (P < 0.005). There was significant difference on distribution of genotype in Parkinson disease group and control group (P < 0.05). The risk incidence increased 3.8 times in individual with T allele. Conclusion: NQO1 gene cDNA 609 mutation T allele may be a risk factor to Parkinson disease, which could be associated with the hereditary susceptibility of Parkinson disease.