514 patients with total hip replacement were operated in 3 years in our county hospital. The patients were divided in two groups: 1. high risk patients: these patients had an antibiotica prophylaxis with 3 doses of 2 g of cefamandole beginning at the time of the induction of the anaesthesia; 2. patients without risks: they had no antibiotica. The two groups of patients were controlled at 3 and 12 months after the operation. 159 patients had a risk for an infection and had antibiotica, 355 patients had no antibiotica. The infection rate after 1 year was 0.6% in the group of patients with antibiotica, and 1.4% in the group of patients without antibiotica. This gave no statistical significance. The only statistical difference between the 2 groups was a significantly higher rate of urinary infection in the group with antibiotica. Thus it has been shown that urinary infections after total hip replacement correctly treated with antibiotica are not a high risk for an infection in the prosthesis. We conclude that antibiotica prophylaxis for total hip replacement in patients with high risk factors (like diabetes, corticotherapy, intraarticular injection, obesity and operation on the same hip) may help to have a postoperatively low infection rate, in our case 0.6%.