Accents provide information about a speaker’s geographical, socio-economic, and ethnic background. An additional important variable in the social evaluation of accented speech is the listener’s own accent. Just as with any in-group marker, there is a preference for accented speakers that sound like us. Here we employed an auditory version of the implicit association test to quantify own-accent bias. At a Welsh university, we recruited two groups of participants born and raised in distinct regions within the UK, Wales and England. These regions have a long-standing history of national rivalry. In Experiments 1 and 2 we show that the magnitude of the implicitly measured own-accent bias in both groups was comparable to biases based on visible group membership (e.g., race). In addition, Experiment 2 shows that this implicitly measured bias was large compared to the explicitly reported preference. The effect sizes of the in-group preference reported here may have societal impact.