Passive chilled beams installed in the perimeter of buildings can be highly effective for off-setting direct solar gains and ensuring good thermal comfort in the perimeter zone. This form of cooling is also potentially more energy efficient than traditional low temperature, chilled water based air conditioning because it uses relatively warm chilled water. This is conducive to high chiller efficiency and also opens up opportunities for designers to specify 'free' or environmental cooling. Unfortunately the performance of perimeter chilled beams has been shown to be very sensitive to the design and configuration of the perimeter area, including suspended ceilings and window blinds. In practice this has often led to poor performance and conflict with architectural and aesthetic requirements. This paper presents the findings of a research project that has investigated the performance of perimeter chilled beams and developed guidance on avoiding the design pitfalls. Mock-up tests investigated the effect of different types of window blinds, the height and shape of ceilings, the presence or absence of ceiling tiles, size of holes in perforated ceiling tiles, the width of the building frame, and the width of the slot at the ceiling perimeter that forms the ceiling void inlet. Illustrations demonstrate the effect of these parameters on the path of the plume of hot air from the perimeter near the windows throughout the room.