This study examined whether patients with major depressive disorder manifest deficits in intelligence during affective episodes and following clinical improvement. WAIS-R scores were contrasted in 100 patients in an episode of major depression with 50 normal controls, matched to the patient sample in terms of demographic variables and estimates of premorbid IQ. The groups were equivalent in verbal IQ, but, in line with previous studies, the depressed patients had a pronounced deficit in performance IQ. A patient subsample was administered the WAIS-R under unlimited time conditions to determine whether the time constraints of performance IQ subtests contributed to the magnitude of the verbal-performance IQ discrepancy. This discrepancy was only slightly reduced with untimed scoring. Subgroups of depressed patients were retested with the WAIS-R within one week (n = 26) or two months (n = 33) following treatment with electroconvulsive therapy. In both subsamples, IQ scores were improved at posttreatment testing relative to pretreatment, but with little change in the verbal-performance IQ discrepancy. These and related findings suggested that a performance IQ deficit is characteristic of depressed patients regardless of affective state.