In this study, I examine whether the mandatory adoption of International Financial Reporting Standards (IFRS) in a country where local Generally Accepted Accounting Principles (GAAP) is of similar quality to IFRS is associated with changes in the comparability of financial statements. I also investigate the sources of any changes in the comparability of financial statements. I use data from South Africa, where, word for word, prior to the mandatory adoption of IFRS, local GAAP was the same as IFRS, and enforcement remained unchanged. I use two different measures of comparability, one based on accounting data (accruals-cash flow measure) and the other based on both accounting data and market data (earnings-return measure). I compare South African firms with two different groups, namely other mandatory IFRS adopters and non-adopters. My data show evidence of an increase in the comparability of the financial statements of South African firms with those of both adopters (both measures) and non-adopters (the earnings-return measure) following the mandatory adoption of IFRS. In additional analysis, I found a global increase in the comparability of firms' financial statements that is consistent with market changes unrelated to IFRS adoption as one of the sources of the increase in comparability. Moreover, an incremental increase in the comparability of the financial statements of South African firms after the mandatory adoption of IFRS, relative to the increase in the comparability of the financial statements of non-adopting firms, is consistent with benefits from using the IFRS "label" and with the expanded IFRS network as sources of increased comparability. / Thesis (PhD)--University of Pretoria, 2017. / Accounting / PhD / Unrestricted