The aim of this study was to evaluate the Parkinson disease (PD) prevalence of cognitive impairment in Taiwan.The case-control study consisted of 6177 cognitive impairment patients and 24,708 noncognitive impairment as controls for the period of 2006 to 2010 and both of the groups aged ≥50 years. The multivariable logistic regression analyses were used to estimate the odds ratio (OR) for cognitive impairment, and the 95% confidence intervals (CIs) among patients with PD were compared with those of non-PD patients.PD (adjusted odds ratio [aOR] is 3.07, 95% CI 2.76-3.41) is the one of the most contributed risk factors for cognitive impairment. Besides, we found a remarkable result of the diagnosed cognitive impairment of PD that was found highest in the first 6 months (aOR 11.98, 95% CI 8.51-16.86) and then decrease the incident year by year. The PD prevalence in a patient with cognitive impairment in our data present is 12.1% lower than those with truly dementia published previously and documented by western studies.We found a remarkable result of the diagnosed cognitive impairment of PD that was found highest in the first 6 months and then decrease the incident year by year.