Several clinical studies have demonstrated that patients with essential tremor (ET) may have cognitive deficits; however, detailed neuropsychological assessments in comparison with motor tasks in patients with ET have not been reported. We conducted a prospective study to determine the correlation of cognition with age, disease duration, and motor task severity in patients with ET. Forty-seven patients with ET who underwent clinical assessment using the Fahn-Tolosa-Marin clinical rating scale and detailed neuropsychological investigation were included. Cognitive decline was significantly correlated with age at the time of examination, educational status, and tremor severity; cognitive decline however, was not related to disease duration or the presence of vascular risk factors. Multiple linear regression analysis revealed that the tremor severity was independently associated with cognitive impairment in patients with ET, regardless of age, gender, educational status, duration of ET symptoms, and vascular risk factors. Our results support the finding that the age at examination and educational status are risk factors associated with dementia in patients with ET, as with other types of dementia. In addition, the relationship between tremor severity and cognitive decline suggests there may be a pathophysiologic association between the two conditions, although the pathologic basis for dementia in the older onset ET cases requires further study.