The longevity of different dog breeds generally declines with size. This has led to the assumption that larger breeds age prematurely. If valid, this represents a significant challenge in canine ethology. The current study used a cognito-behavioural survey of older dog (>8 years) owners to explore five broad domains: ingestion; locomotion; owner interaction; housesoiling; and aggression. Questions (n=84) were designed to capture the frequency of behavioural responses and also any change in frequency over the previous 6 months. After dogs with neurological or cognitive disorders were excluded, scaled survey responses from normally ageing dogs (N= 623. representing 100 breeds, from 11 countries) were dichotomised and analysed using binary logistic regression to correct for age. When split into three breed longevity categories, the percentage of longer-lived breeds showed a high frequency of: post-prandial hunger; hypodipsia; aggression; and avoidance of their owners was 13.8, 13.4, 17.2 and 6.8% higher (p<0.05) respectively than short-lived breeds. When split into three breed size categories, dogs in the large-breed group showed aggression or fearfulness 7.7 and 10.6% less frequently (p<0.05) respectively than those in the small-breed group. Reported increases in aggression or time spent eating were also 7.3 and 2% less likely respectively. Conversely, the percentage of larger breeds showing: polydipsia; minimal activity; walking into walls; grooming conspecifics; and reported declines in obedience was 49.9, 7.3, 3.8, 7.6 and 13.9% higher (p<0.05) than small breeds. Interestingly, despite some increases in disease (reported elsewhere), aged short-lived and large breeds (i.e. those assumed to age prematurely) had fewer reported unwelcome behaviours. Overall the high percentage of unaffected behaviours in both analyses (92% and 87% respectively) suggests that cognito-behavioural ageing does not affect dog breeds at different rates. The apparent absence of variability between size and longevity groups should facilitate the study of canine senescence in the community.