The purpose of this study is to contrast the level of information disclosed by Spanish companies during and after the transition to the IAS/IFRS (International Accounting Standards/International Financial Reporting Standards). We have selected information about pensions provided by the companies quoted in the IBEX-35 (Index of Stock-Market of Madrid). Before the transition to the new set of standards, this information was voluntary, but after the transition, the information to disclose became compulsory. Thus, we have analysed the level of fulfillment of rules in the elaboration of the annual report. The methodology used for this study is quantitative. First, through a content analysis, we have studied the information on pension funds that discloses the companies quoted in the consolidated annual report once the IAS/IFRS has been adopted. Second, through a multivariate analysis, we have contrasted our results. Thus, we aim to determine the causes of the variation of the information supplied by the companies. The results suggest that after controlling size, sector and the existence of post-employment obligations, the disclosure quality and extent are positively associated with the enforcement of the accounting regulation.