Background: Electroconvulsive therapy (ECT) remains the most effective and fast-acting treatment option for several psychiatric conditions, including treatment-resistant depression. Although ECT has been in use for 75 years, the mechanism of action is unknown. There is emerging evidence that modulation of the hypothalamic-pituitary-adrenal axis may mediate, in part, the therapeutic action of ECT. A growing body of evidence points to links between disturbances in the immune system and depression. However, the impact of ECT on immune functioning and the possible role of alterations in the immune system as a mechanism of action of ECT remain elusive. Objectives: To provide a literature overview on the effects of ECT on the immune system. Methods: Relevant articles and abstracts in English were retrieved from PubMed/Medline using search terms related to ECT, inflammation, and immune system. The results of studies examining ECT-induced changes in immune functioning as well as the degree to which these represent possible mechanisms mediating the therapeutic action of ECT were summarized. Results: Our search identified only a limited number of studies. The findings suggest that a single session of ECT induces an acute, transient immune activation, whereas repetitive ECT treatment results in long-term down-regulation of immune activation. However, inconsistency in findings and methodological issues, including sample size and lack of consideration of confounding factors affecting cytokine concentrations, precludes definitive conclusion. Conclusions: To elucidate the possible role of immunological changes mediating the effect of ECT, more prospective controlled studies with larger sample sizes are required.