The incidence of infections in general surgery is related to different factors. Cost-benefit analysis of antimicrobic prophylaxis is positive, even though incorrect use may be even dangerous (development of resistance and/or superinfections, for instance). The authors report data on a study concerning a total of 316 patients divided into two series, who had antimicrobic prophylaxis before a surgical operation. 274 patients out of 316 (or 86.7%) had an ultra-short (one-shot-only) or short (<24 hours) prophylaxis, 42 (13.3%) standard (>24 hours). The operations performed were classified following class of contamination, i.e. I (clean), II (potentially contaminated), III (contaminated). Antibiotics used were ceftizoxime, cefepime, ceftriaxone, piperacillin and gentamicin in combination. A total of 16 postoperative infections was observed (5%); 11 of these 16 belonged to class III operations. Escherichia coli and Staphylococcus aureus were isolated in most of the infected wounds. The data confirm what is reported in the literature. The authors conclude that a preoperative single-shot 3rd or 4th generation cephalosporin reduces the incidence of wound infections in clean and clean-contaminated surgery.