Aggression between dogs is common and can result in injury. The aims of this study were to estimate prevalence, evaluate co-occurrence with human-directed aggression, and investigate potential risk factors, using a cross-sectional convenience sample of dog owners. Aggression (barking, lunging, growling or biting) towards unfamiliar dogs was reported to currently occur, by 22 per cent of owners, and towards other dogs in the household, by 8 per cent. A low level of concordance between dog and human-directed aggression suggested most dogs were not showing aggression in multiple contexts. Aggression towards other dogs in the household was associated with increasing dog age, use of positive punishment/negative reinforcement training techniques, and attending ring-craft classes. Aggression towards other dogs on walks was associated with location of questionnaire distribution, owner age, age of dog, origin of dog, dog breed type, use of positive punishment/negative reinforcement training techniques and attending obedience classes for more than four weeks. In both, the amount of variance explained by models was low (<15 per cent), suggesting that unmeasured factors mostly accounted for differences between groups. These results suggest general characteristics of dogs and owners which contribute to intraspecific aggression, but also highlight that these are relatively minor predictors.