Mental health within the professional services industry in Hong Kong is a concern. However, little is known about the cost of mental ill health to the economy. The City Mental Health Alliance Hong Kong and Oliver Wyman have collectively piloted and effort based on available data to estimate the potential size of the issue and the cost to business. Mental ill health cost to employers is estimated at HKD 5.5-12.4 BN per year, driven by absenteeism, presenteeism and turnover. The aim of the report is to raise understanding and awareness, encourage employers to consider putting in place appropriate measures to support employee mental health and encourage further research and debate. Empirical studies from other markets and even in Hong Kong suggest that there are typically positive pay-off for investing in mental health support programs.