Cognitive impairment of mild-to-moderate severity is known to occur among a large proportion of patients with multiple sclerosis (MS). Depressive affective disturbances are also known to occur commonly among these patients. In order to determine the degree of interaction between mood disturbance and cognitive impairment, we conducted a test- retest neuropsychological study of 11 MS patients with current major depression diagnosed by Research Diagnostic Criteria. Patients were tested while depressed and at another point while euthymic. Nine patients were assessed first in a depressed state, followed by a reevaluation in the euthymic state, and two were assessed first in the euthymic state. The mean time interval between assessments was 7 months. When cognitive performance in the depressed condition was compared with cognitive performance in the euthymic condition, no significant differences were found. There was evidence for a pattern of improvement in verbal memory tests that fell short of statistical significance. Some language-related cognitive functions actually deteriorated during the 6-month course of this study.Abstract Teaser