Background: Morbid obesity and malnutrition have both been demonstrated to have deleterious effects on the immune function. Cytokines are immunomodulatory peptides that have profound effects on immune function. To the authors' knowledge, the effect of surgically induced weight reduction on the cytokine levels has yet not been studied. In the present study, the authors determined the effect of surgically induced weight reduction on the levels of the cytokines interleukin-3 (IL-3) and tumor necrosis factor-α (TNF-α). Methods: 14 patients undergoing silicone ring vertical gastroplasty were included in the study (mean BMI 48.85 kg/m2; range 38.1-52.0 kg/m2). Determination of the IL-3 and TNF-α levels was performed preoperatively and 14 days and 6 months postoperatively, when all patients had lost 25% to 30% of their preoperative weight. Results: The IL-3 values before the procedure, and 14 days and 6 months after, were as follows: 9.69 ± 1.82, 9.36 ± 1.28, and 8.42 ± 1.26 pg/mL, respectively (P < 0.05 preoperative versus 6 months postoperative level). The preoperative TNF-α levels showed a wide distribution. For this reason, the patients were divided into two groups: Group A with preoperative values >10 pg/mL and Group B with values P < 0.05). In Group B, the TNF- α levels were not significantly changed and were 5.45 ± 2.26, 7.59 ± 4.56, and 8.82 ± 6.27 pg/mL, respectively. Conclusion: The present study demonstrates a significant decrease in the levels of the cytokines, IL-3 and TNF-α. These changes can be responsible for alteration of the immune function after surgically induced weight reduction.