To investigate whether the cumulative number, duration and subtypes (severity and presence of psychotic features) of previous episodes of depression in patients with unipolar depressive disorder in a remitted state are associated with decreased global cognitive function.

Via the Danish registers individuals between 40 and 80 years of age were identified: (1) patients with a diagnosis of unipolar disorder at their first discharge from a psychiatric hospital in the period 1994 to 2002, and (2) gender and age matched control individuals. The participants were assessed with the Cambridge Cognitive Examination (CAMCOG), which provides a composite measure of global cognitive function.

A total of 88 patients and 50 controls accepted our invitation to participate, fulfilled the selection criteria and were included in the study. The cumulative duration of depressive episodes was associated with a decreased CAMCOG score adjusted for age, gender, education, premorbid IQ and residual depressive symptoms (B = −0.14, 95% C.I. (−0.26, −0.02), R2adj = 0.31, P = .02). Significant associations were also found between CAMCOG score and the cumulative duration and total number of depressive episodes with psychotic features, respectively.

Our findings suggest that cognitive dysfunction is associated with the cumulative duration of depressive episodes, and that, in particular, depressive episodes with psychotic features in the course of illness may be a significant predictor of future impairment of cognitive function.