background Late onset disorders are often associated with cerebral disfunctioning and cognitive impairment in elderly patients. It is unknown if age of onset affects cognition in bipolar disorder.
aim The authors compare cognition and clinical characteristics of early and late onset bipolar patients in a stable and euthymic condition. 
methods 119 older patients (age >60) with an early (<40 years) or late onset bipolar disorder and a group of 78 comparison subjects were extensively tested on cognitive functioning.
results Bipolar subjects scored lower on most cognitive measures compared to normal subjects. Late onset patients were more impaired on psychomotor performance and executive functioning than early onset patients. A number of factors are analysed that may explain the differences in cognitive functioning, such as cerebrovascular risk factors.
conclusions Cognitive impairments play an important role in older patients with bipolar disorder. Special attention should be given to late onset bipolar disorder. For clinical practice it is important to develop more suitable pharmacological and psychological interventions to improve cognitive impairment.