Background. A review of studies of cognition in the euthymic phase of unipolar and bipolar affective disorder reveals diverging results.

Methods. The study was designed as a controlled cohort study, with the Danish psychiatric case register of admissions used to identify patients and the Danish civil register to identify controls. Patients who were hospitalized between 19 and 25 years ago with an affective diagnosis and who at interviews fulfilled criteria for a primary affective unipolar or bipolar disorder, according to ICD-10, were compared with age- and gender-matched controls. Interviews and assessment of the cognitive function were made in the euthymic phase of the disorder. In all, 118 unipolar patients, 28 bipolar patients and 58 controls were included. Analyses were adjusted for differences in the level of education and for subclinical depressive and anxiety symptoms.

Results. Patients with recurrent episodes were significantly more impaired than patients with a single episode and more impaired than controls. Also, within patients the number of prior episodes seemed to be associated with cognitive outcome. There was no difference in the severity of the dysfunction between unipolar and bipolar patients.

Conclusions. Cognitive impairment in out-patients with unipolar and bipolar disorder appears to be associated with the number of affective episodes.