This study develops a transparency index to measure the quality of disclosure of corporate governance practices of major Hong Kong listed companies, based on the OECD principles of corporate governance. Using time series data over a three-year period, we show that company valuation is positively associated with the quality of company disclosure. The index is further split into two sub-indexes, voluntary and non-voluntary disclosure, based on the disclosure requirements amended by the Hong Kong stock exchange in 2004. The findings support the hypothesis that company valuation is positively associated with a company’s level of voluntary disclosure. Hong Kong listed companies with larger size, better profitability, a remuneration committee, more outside directors, and that are non-China related tend to have a higher level of voluntary disclosure.