SUMMARY
This article examines the variables that influence the decision of firms to adhere to the Corporate Sustainability Index of the São Paulo Stock Exchange (Bovespa). We investigated the following variables: firm size, sector of activity, shareholding concentration, location of controlling shareholder, issuance of ADRs and public-sector versus private-sector control. The initial data came from selecting the 150 most liquid shares listed for trading at the BM&F Bovespa, with transactions during at least 50% of the trading sessions in the period from June 2006 to June 2007. From these, we chose 124 firms to compose the final sample, which we classified into firms included and not included in the hypothetical portfolio making up the sustainability index from December 2007 to November 2008. We applied the logit multiple linear regression model to assess the contribution of each variable to explain the chance of adhering to the index. The results suggest there is a statistically significant indication that size and sector influence this inclusion, while the other variables statistically did not have any influence. Key words: corporate social responsibility, corporate sustainability, sector of activity, firm size.