Natural ventilation driven by the combined forces of wind and buoyancy has been studiedexperimentally for a building flanked by others forming urban canyons. The steady ventilationestablished in an isolated building was observed to change dramatically, both in terms of the thermalstratification and airflow rate, when placed in the confines of an urban canyon environment. Theresulting ventilation flows and internal stratifications are presented for different combinations of windspeed, opening area and location, and canyon width (building density). Flanking an otherwise isolated building with others of similar geometry in a typical urban canyon geometry is shown to reverse the effect of wind on the buoyancy-driven ventilation. The implications on thermal comfort and design guidance are discussed.