Vagus nerve stimulation (VNS) has gained increasing acceptance for treatment of drug-resistant seizures. The aim of this study was to evaluate effects of VNS on depressed mood in epilepsy patients during the first 6 months after implantation of the stimulation device. This study was conducted as an addition to the international multisite randomized and double-blind controlled trial on anti-seizure effects of VNS (EO3). Only adult patients with >4/month medication-resistant complex-partial seizures were included (N=11). During the acute phase of the study (3 months after implantation), patients were randomly assigned to low (stimulation detection) versus high stimulation (maximal tolerability, maximum 1.75 mA). Mood and mood changes were recorded based on standardized psychiatric rating scales and self-report questionnaires. Patients were assessed 4 weeks before (baseline) as well as 3 and 6 months after implantation. Significant positive mood effects were observed in most scales and subscales at the 3-month follow-up (P<0.05). Mood improvements were sustained at the 6-month follow-up and were independent of effects on seizure activity (9/11 mood responders versus 2/11 seizure responders). Mood effects appeared more pronounced in the high stimulation group after the acute study phase, but findings were not significant (P<0.10). VNS is associated with mood improvements in patients with epilepsy, but to confirm VNS dose effects, studies with more statistical power are needed.