BACKGROUND: Based on improvements in indoor environmental quality claims are that 'green' buildings are healthier and promote greater productivity than conventional buildings. However, the empirical evidence over the last decade has been inconclusive, usually with flawed study designs. OBJECTIVE: This study explored whether a 'green' building leads to a healthier, more productive work environment. METHODS: A one-year, longitudinal comparison of two groups of employees of a large commercial bank; a group that moved into a GreenStar-accredited building and a group that stayed in a conventional building, was conducted. Measures of psychological wellbeing, physical wellbeing, productivity, and perceptions of the physical environment were taken before the move, six months later, and one year later. RESULTS: Results indicate that the 'green' building group had significantly increased self-reported productivity and physical wellbeing. The perceptions of the physical work environment indicate that respondents in the 'green' building group experienced significant air quality improvements (specifically, reduced stale air, better ventilation, improved air movement, reduced humidity, and conditions that were not too drafty) but perceived the lighting conditions as dimmer. CONCLUSION: Despite positive findings 'green' building rating tools require amendment to focus on those qualities that actually lead to improved wellbeing and productivity.