The owner's behaviour is regarded to be a possible cause of unfavourable behaviour such as poor obedience or excitability in smaller dogs. The aim of this study was to investigate whether owner behaviour such as use of training methods, inconsistency in the owner's behaviour or engagement in shared activities differs between owners of smaller (<20 kg) and larger dogs (>= 20 kg) and whether associations between the owner's and the dog's behaviour in smaller dogs differ from those in larger dogs. For this Purpose, a questionnaire-based survey via postal mailing was conducted in an urban and suburban population of pet dog owners (response rate: 28%). Statistical analysis of 1276 questionnaires involved descriptive statistics, Chi(2)-test, t-tests and Spearman correlations. Our results confirm that smaller dogs are seen as less obedient (P<0.001), more aggressive and excitable (P < 0.001) and more anxious and fearful (P < 0.001). Smaller dog owners reported being more inconsistent in interactions with their dog (P < 0.001) and engaging less in training and play activities (P<0.001) than larger dog owners. More consistent owner behaviour (r(s) = -0.4, P<0.001) and more frequent engagement in training and play activities (r(s) = 0.4, P < 0.001) correlated with better obedience in smaller dogs. No marked differences were found in the types of training methods used with smaller and larger dogs, but owners of smaller dogs reported slightly less use of punishment (P = 0.007). In smaller and larger dogs, a more frequent use of punishment was associated with increased aggression and excitability (smaller: r(s) = 0.3, P < 0.001; larger: r(s) = 0.2, P < 0.001) as was a more frequent use of reward-based responses to unwanted dog behaviour such as calming or distracting the dog (r(s) = 0.2, P < 0.001). The main result of our study was that increased anxiety and fear was related to a more frequent use of punishment in smaller (r(s) = 0.2, P < 0.001) but not in larger dogs. We conclude that smaller dog owners could significantly improve obedience in their dogs by being more consistent in interactions and engaging regularly in play and training activities with them. Behavioural problems could be reduced by avoiding habits of punishment that might reinforce fear or fear-related aggression. (C) 2010 Elsevier B.V. All rights reserved.