The Pit Bull Terrier (a.k.a. American Pit Bull Terrier or Pit Bull) has acquired a universal reputation for aggressiveness, prompting breed bans in countries, regions, and municipalities throughout the world. Despite adverse public perceptions and policies, there is a lack of reliable scientific evidence that Pit Bull Terriers are behaviourally different from other common breeds of dog. To investigate possible behavioural differences between Pit Bull Terriers and other breeds, the present study used behavioural data collected from a convenience sample of dog owners via the online Canine Behavioral Assessment & Research Questionnaire (C-BARQ: http://www.cbarq.org). The C-BARQ is a validated survey instrument with adequate reliability characteristics that is designed to measure the prevalence and severity of 13 major categories of behavior problem in dogs (Hsu & Serpell, JAVMA, 223: 1293, 2003). Although potentially subject to self-selection bias, the findings showed that Pit Bull Terriers (N=139) obtained significantly higher (worse) scores for the C-BARQ factor "aggression toward other dogs" (Mean = 1.301, SE = 0.0956) than a combined sample (N=7384) of other breeds (Mean = 0.871, SE = 0.011; Mann-Whitney U = 395142.00, P < 0.0001), although two other breeds-the Akita and Dachshund-were equally aggressive in this context. Contrary to expectations, Pit Bull Terriers did not obtain significantly higher scores for either "owner-directed aggression" or "stranger-directed aggression" compared with the other breeds surveyed, although they were more likely to bite unfamiliar persons (c2 = 5.392, P < 0.05). This last effect disappeared, however, when certain background factors (e.g. source of acquisition) were taken into account. Possible reasons for the apparent mismatch between public perceptions and the present findings are discussed.