Responsible companion animal guardianship (RCAG) covers aspects that are relevant to both animal and human health. Understanding the factors associated with adherence to RCAG principles can guide accountability, animal welfare and disease control. The present observational study describes the level of adherence to RCAG by guardians living in a medium-sized Brazilian municipality and identifies the factors associated with inadequate guardianship. Questionnaires were administered to randomly selected guardians of 704 dogs. The binary outcome of the study, namely more and less adequate compliers to RCAG principles, was analyzed using a score list comprising eight variables relating to the care provided to the dogs, namely provision of veterinary services, vaccination against rabies, deworming, no access to the streets without supervision, walking with guardian, dog freedom at home, registration (microchipping) and satisfactory food supply. Factors possibly associated with less adequate adherence to RCAG by the guardian, such as socioeconomic and cultural features of the guardians, characteristics of the dogs and attributes of the guardian-animal interactions, were analyzed using multiple logistic regression models. The RCAG actions least adopted by guardians were animal registration, provision of veterinary care, walking with the dog and preventing access of the dogs to the streets without supervision. Individuals who cared for a single dog, a mixed breed dog or had previously lost a dog were less likely to show adequate adherence to RCAG. Conversely, guardians who owned cars, acquired dogs as puppies, lived in households with a maximum of four residents, cared for a sterilized dog or thought that caring for a dog was easier than (or as) expected, had a higher chance of showing adequate adherence to RCAG. The results verify that the socioeconomic and behavioral characteristic of guardians must be taken into consideration for understanding the adherence to RCAG. In addition, it is important to facilitate access to veterinary services and to raise awareness about the significance of a safe and healthy environment for companion animals.