<p>Dementia is one of the most significant non-motor symptoms in Parkinson’s disease (PD), particularly in the advanced stages. Identifying predictive factors for cognitive decline in PD is crucial for optimizing intervention strategies, improving prognosis. However, few studies have focused on long-term PD (L-PD) patients with dementia (L-PDD). A total of 330 PD patients were recruited from the movement disorder clinics at three tertiary hospitals in China. The cohort included 201 long-term PD patients without dementia (L-PDN) and 66&#xa0;L-PDD patients with disease duration greater than 10 years, as well as 63 patients with short-term PDD (S-PDD) with disease duration less than 10 years. Data on demographic and clinical characteristics were collected. T-test and Mann-Whitney U test, Spearman’s correlation, and stepwise multiple linear regression were employed for data analysis. The average disease duration, age at interview and age of onset of the L-PD patients were 13.19 ± 3.43, 66.46 ± 7.81 and 53.26 ± 8.41 years, respectively. And the average disease duration, age at interview and age of onset of the S-PDD patients were 4.41 ± 2.48, 66.97 ± 7.88 and 62.56 ± 8.00 years. Compared with L-PDN, L-PDD patients had more advanced motor and non-motor symptoms including severe hyposmia, lower education level, which constructed a good linear regression model with the variable of dementia. In the L-PDD group, MMSE scores were correlated with both education duration and SS-16 scores (16-item odor identification test of Sniffin’ Sticks). However, no significant correlation between SS-16 scores and MMSE scores was observed in either the L-PDN or S-PDD groups, despite the presence of severe hyposmia in the S-PDD group. The present study suggests that lower education levels and hyposmia are risk factors for L-PDD, with the severity of hyposmia potentially correlating with both the development of PDD and the degree of cognitive impairment in L-PDD.</p>