The relationship between familiarity, public participation and environmental preferences is examined using an urban design case study. Previous research has shown that familiarity judgements certainly play a role in preference judgements. Generally speaking, greater degrees of actual familiarity are considered to increase affective responses to environmental scenes. In addition to the degree of actual familiarity, there is evidence to suggest that the degree of perceived familiarity influences preference in the same direction. However, when dealing with the design of the built environment, we are often asking people to compare an existing environment with an environment that has yet to be realised (i.e. a design). The degree of actual familiarity with a design is necessarily low for most people (apart from for the designer), but clearly the degree of perceived familiarity may be high. With this in mind, we designed a study to investigate the role that both actual and perceived familiarity had on people’s comparisons between an existing urban square and a proposed re-design of that space. The design used was the result of an extensive public consultation study reported elsewhere. Actual familiarity with the square was manipulated by using two samples: one (N=100) from the same city as the case study, and one (N=100) from a different city. The framing of the presentation of the design scenario was also manipulated, so in one condition participants were told that the design was the most popular option with local residents arising from a public consultation looking at 9 possible design scenarios, and in the other condition they were simply told that the local authority were considering the design. Participants were presented with colour images taken from photorealistic computer models of both the existing situation (an urban square being used as a car park), and a re-designed scenario (which involved removal of vehicular traffic from the square). After viewing each image, participants rated the scene on a number of semantic differential scales, and were asked to state what they liked and disliked about the scene. Participants were also asked to state the degree to which the re-designed scenario was better or worse than the present situation. Results are analysed and presented, and both the theoretical and applied implications are discussed.