This prospective study was performed to evaluate the relationship between interleukin-6 (IL-6), oxidative stress and sperm function following vasectomy reversal. We included 22 patients who underwent vasectomy reversal and 15 healthy sperm donors (controls) with normal sperm morphology criteria. Levels of IL-6 in the semen were measured by the enzyme-linked immunosorbent assay, and levels of reactive oxygen species (ROS) and total antioxidant capacity were measured by the chemiluminescence assay. The mean sperm concentration in the vasectomy reversal group was significantly lower than control group (45.3 +/- 39.1 versus 63.1 +/- 28.5; P = 0.02). Motility was also significantly lower in the vasectomy reversal group (32.1 +/- 19.9 versus 54.6 +/- 18.9; P = 001). Levels of IL-6 were significantly higher in the vasectomy reversal group (2.09 +/- 0.87 versus 0.99 +/- 0.97; P = 0.007) as were mean ROS levels (2.25 +/- 0.97 versus 1.2 +/- 0.7; P = 0.009). Significant positive correlation was observed between the IL-6 and ROS levels in vasectomy reversal patients compared with donors (r = 0.41, P = 0.05 versus r = 0.38, P = 0.15). We conclude that patients who undergo vasectomy reversal have elevated levels of IL-6 and ROS, which may contribute to decreased sperm motility and concentration and possibly lead to sub-fertility.