Hong Kong is a densely populated city where a significant proportion of the population lives in highly urbanised areas. During the summer months conditions in Hong Kong are generally hot and humid and can get quite oppressive, the added burden of the urban heat island (UHI) can intensify these conditions. The urban thermal environment varies not only from its surroundings but also within the urban area due to intra-urban differences in land-use and surface characteristics. To investigate the UHI in Hong Kong, vehicle based temperature and relative humidity traverses were used to determine spatial differences in the summertime UHI across the city. A total of 29 vehicles traverses were undertaken during the coolest and/or hottest part of the day across eight days during May-June 2008. From these meteorological measurements and associated Geographical Information System (GIS) resources we have determined the land-use and surface characteristics associated with peaks in the UHI. The hottest regions within the Hong Kong urban area are often associated with areas of extremely high population density; therefore the issue of exposure to the UHI will be presented. Socio-economic and demographic data from the latest Hong Kong census was used to quantify exposure and vulnerability to the UHI among different Hong Kong resident populations.