Objective. Evaluation of the effectiveness of a standard dose of cefalozin 2 grams for surgical site infection (SSI) prevention in obese patients compared to non-obese patients. There is no still controversy surrounding which is the best dosage of this antibiotic in obese patients for surgical prophylaxis. Material and methods. Retrospective review of men who received prophylactic cefazolin between January 1st, 2019 and June 30th, 2019 in a traumatology department of a university hospital. Patients were stratified into 2 groups: obese (≥ 100 kg and body mass index (BMI)> 30 kg / m2) and non-obese. Patients without a 90 days follow-up after surgery and/or with an active infection at the time of surgery and/or treated with immunosuppressants were excluded. Demographic data, height, real weight, smoking, diabetes, concomitant use of immunosuppressants, surgery data and presence of infection until day 90 were collected. Results. A total of 57 patients underwent traumatic surgery with prophylactic cefazolin, 26 non-obese and 23 obese, were studied. Both groups presented statistically significant differences in weight, BMI and post-surgery use of cefazolin. No significant differences were observed in the other variables. Two obese (8.7%) and two non-obese (7.7%) patients developed SSIs after 63 days post-surgery on average, following the difference between the groups being statistically non-significant. Conclusion. This study shows that there is no significant difference in SSI with a standard prophylactic dose of two grams of cefazolin between obese and non-obese patients.