BACKGROUND: Executive impairments have been reported in affective illness, but the influence of attention on executive performance has not been fully considered. The purpose of this study was to investigate whether executive impairments in affective illness were independent of attention impairments, and whether independent executive impairments were specific to bipolar (BP) affective illness. METHOD: Forty-two individuals with major affective disorders [20 unipolar (UP) depression and 22 BP disorder] were compared with 40 healthy controls on measures of attention and executive function. None of the patients were currently experiencing an episode of affective illness. RESULTS: As expected, both UP and BP patient groups showed significant neuropsychological impairments relative to controls. Significant differences in performance on executive function measures were also observed between UP and BP patients, even after the influence of attention had been taken into account. These impairments were not attributable to current levels of affective symptomatology or to medication. CONCLUSIONS: A single neuropsychological dissociation appears to be present between UP and BP affective illness, with BP individuals showing a specific executive deficit that is independent of attention impairment on the Hayling Sentence Completion Test (HSCT).