We assess the impacts of operative delivery for the first twins with vertex presentation on neonatal outcomes in second twins using the 1995 to 1997 twin registry data of the United States. A total of 102,554 eligible twin pairs with vertex presentation for the first twin were included in the analysis. Of these, 50,748 (49.5%) first twins had a normal vaginal delivery, 43,504 (42.4%) were delivered by cesarean section, and 8302 (8.1%) were delivered by vaginal operation (vacuum extraction or forceps). In term twins, the risks of asphyxia-related mortality (odds ratio [OR], 3.08; 95% CI, 1.07 to 8.45), newborn injury (OR, 2.10; 95% 1.39 to 3.12), low Apgar score at 5 minutes (OR, 1.49; 95% 1.24 to 1.78), and mechanical ventilation use (OR, 1.34; 95% 1.20 to 1.51) were increased in the second twins whose co-twins were delivered by vaginal operation compared with those whose co-twins who had normal vaginal delivery. In contrast, the risks of asphyxia-related mortality (OR, 0.55; 95% 0.17 to 1.57), newborn injury (OR, 0.20; 95% 0.11 to 0.34), low Apgar score at 5 minutes (OR, 0.51; 95% 0.44 to 0.60), and mechanical ventilation use (OR, 0.77; 95% 0.71 to 0.83) were decreased in the second twins whose co-twins were delivered by cesarean section compared with those whose co-twins had a normal vaginal delivery. In conclusion, vaginal operative delivery for the first twins is related to the adverse neonatal outcomes of their co-twins, whereas cesarean delivery for the first twins is associated with the beneficial neonatal outcomes of their co-twins.