Objective To investigate the association between hyperhomocysteinemia and cognitive impairment in Parkinson's disease. Methods A total of 130 patients with Parkinson's disease who were admitted to our hospital were selected as the experimental group, and 110 healthy persons who underwent physical examination during the same period were enrolled as the control group. A logistic regression analysis was performed to identify the possible risk factors for cognitive impairment, and the serum level of homocysteine was compared between the patients with mild cognitive impairment, the patients with dementia, and healthy controls.Results The unconditional logistic regression analysis showed that age, educational level, smoking, hypertension, diabetes, high-density lipoprotein, low-density lipoprotein, serum total cholesterol, and plasma homocysteine were risk factors for cognitive impairment. Compared with the Parkinson's disease patients with or without cognitive impairment, the control group had a significantly different level of plasma homocysteine (t=3.45, P<0.05; t=6.43, P<0.05). The level of plasma homocysteine showed a significant difference between the Parkinson's disease patients with and without cognitive impairment (t=5.23, P<0.05).Conclusions The Parkinson's disease patients with cognitive impairment have a higher level of homocysteine than those without cognitive impairment and healthy persons. Hyperhomocysteinemia is the risk factor for cognitive impairment in Parkinson's disease and can be used as a reliable indicator for diagnosis.