Understanding the factors associated with post-adoptive return in dogs (Canis familiaris) is important for reducing shelter return rates. The objective of this retrospective study was to identify factors detectable in shelters associated with post-adoptive return in an objective dog-centric analysis. The records of 959 dogs were evaluated via factor analysis of seven behaviour and seven physical variables which resulted in the extraction of six principal factors. Fear aggression, ongoing health concerns, separation anxiety, sex-specific aggression, and age effect on source were not found to significantly impact outcome. In particular, dog aggression risk (a factor composed of breed, size, and dog aggression) was found to be significantly higher in returned dogs. Since dog aggression risk is associated with post-adoptive return, this could help shelters to modify policies to either screen aggressive dogs from the adoption population or improve adoption counselling in an attempt to help lower return rates.