A study was conducted to assess whether antibiotic prophylaxis in low-risk patients for post-cesarean febrile morbidity was beneficial and cost effective. In a randomized, prospective study, 167 patients received a single, 1-g dose of cefazolin before clamping of the cord, and 140 did not. In the group given prophylaxis the febrile morbidity and postoperative therapeutic antibiotic usage were significantly lower than in the group not given prophylaxis (9% vs. 17.9%, P = .035, and 6.5% vs. 20%, P < .001, respectively). We conclude that single-dose cefazolin prophylaxis is both beneficial and cost effective, even in patients considered to be at low risk of post-cesarean febrile morbidity. Since the value of antibiotic prophylaxis in high-risk patients is accepted, universal antibiotic prophylaxis in every cesarean section case is suggested.