This paper reports the results of a pre-test post-test intervention study that aimed to encourage energy conservation behaviour by office workers at a large Australian hospital. Using visual prompts and top management support for energy conservation behaviour, significant long-term improvements were made for behaviours with individual responsibility. However, for behaviours with collective responsibility the results were mixed. Energy audits were used as an objective measure of behaviour change. Additionally, pre- and post-intervention surveys revealed significant changes in self-reported behaviour, perceived top management support, perceived internal environmental orientation, norms, and knowledge regarding energy conservation behaviour. The findings suggest that different intervention strategies may be required depending on whether the targeted behaviours have collective or individual responsibility.