Aggression is the most common dog behavioral problem, with important implications for public health. The aim of this study was to determine the perception of veterinarian clinicians of Montevideo regarding canine aggression, the sex effect, and the main breeds involved. One hundred veterinary clinics of Montevideo city were randomly selected to complete a survey about aggressiveness in dogs. Most veterinarians opined that males are more involved than females in canine aggression and that the Pit bull, the German Shepherd, and Uruguayan Cimarron breeds were the most involved in both types of aggression considered (between canines and towards people), while the Cocker Spaniel breed was involved in aggression towards humans and the Rottweiler breed in aggression between dogs. This work highlights that both veterinarians and other experts within the community identify the Uruguayan Cimarron as being aggressive, which indicates that the behavior of this breed may be of particular concern.