Neurodegenerative disease in patients with chronic obstructive pulmonary disease (COPD) was observed. We aim to clarify the risk of dementia in patients with COPD. The study used claims data from Taiwan's National Health Insurance Research Database. Subjects were those who received a discharge diagnosis of COPD between January 1, 2002 and December 31, 2011. Only the first hospitalization was enrolled, and the index date was the first day of admission. Patients younger than 40 years or those with a history of Alzheimer disease (AD) or Parkinson disease (PD) before the index date were excluded. The patients with COPD were then followed until receiving a diagnosis of AD or PD, death, or the end of the study. Control subjects were selected from hospitalized patients without a history of COPD, AD, or PD and were matched according to age (±3 years), gender, and the year of admission at a 2:1 ratio. The comorbidities were measured from 1 year before the index date based on the ICD-9-CM codes. The study included 8640 patients with COPD and a mean age of 68.76 (±10.74) years. The adjusted hazard ratio of developing dementia (AD or PD) was 1.74 (95% confidence interval = 1.55-1.96) in patients with COPD compared with patients without COPD after adjusting for age, gender, and comorbidities. This nationwide cohort study demonstrates that the risk of dementia, including AD and PD, is significantly increased in patients with COPD compared with individuals in the general population.