Pesq. Vet. Bras. 33(6) Hospital or nosocomial infections are infections acquired during patient hospitalization, and that can be related to surgical and invasive procedures performed during the hospital admission. The present study aimed to investigate the occurrence of nosocomial infection in animals treated at a Veterinary Surgical Center of Small Animals, submitted to surgical or invasive procedures, to discuss the possible causes of infection, to detect the bacteria present when possible, and to verify the antimicrobial sensitivity of these agents. The study was developed through daily monitoring of 131 animals admitted in this surgical center and doing active surveillance of cases of nosocomial infection. In 104 animals (91 dogs and 13 cats), 113 surgical procedures were performed, and in 27 animals were performed non-surgical procedures such monitoring of delivery and postpartum, urethral catheterization and placement of splints. All animals were submitted to catheter placement for fluid therapy and application of medications and/or anesthetic at some point during hospitalization. The rate of surgical site infection was 7.96%, and by categories was 4.54% in clean surgeries, 4.25% in clean-contaminated surgeries, 10.53% in contaminated surgeries, and 16% in infected surgeries. The rate of non-surgical nosocomial infection in surgical patients was 2.88% and in the non-surgical patient was 3.7%. Bacteria were cultured as follows: Pseudomonas sp. (3), Streptococcus sp. (2), Acinetobacter sp. (1) and Gram negative bacilli (1), and high bacterial multidrug resistance were observed in all isolates. The duration of surgery and pre and postoperative time of hospitalization did not affect the occurrence of nosocomial infection, but factors that probably contributed to the occurrence of infections in this study were the severity of the condition responsible for the treatment, the kind of procedure performed and the severity of lesions.