This paper investigates the effect of the 2009 guidance of the Department for Environment, Food & Rural Affairs on greenhouse gas (GHG) disclosure. The sample comprises 215 companies from a population of London Stock Exchange FTSE 350 companies over four years (2008e 2011). To quantify GHG disclosure, a research index methodology is employed, with information derived from several GHG reporting frameworks. The econometric model is estimated using panel fixed effects. Our findings suggest that the publication of the 2009 guidance has had a significant effect on the level of GHG disclosure, and that corporate governance mechanisms (board size, director ownership, and ownership concentration) also affect the extent of GHG information disclosure. The results also indicate that companies increased their disclosures prior to the 2009 guidance in anticipation of its publication. These results have important implications for the government, suggesting that non-mandatory guidance could increase disclosure as much as do mandatory requirements