This study determines whether voluntary adoption of IFRS is associated with increased comparability of accounting amounts and attendant capital market benefits. After “adopting” firms voluntarily adopt IFRS, their accounting amounts become more comparable to those of firms that “adopted” IFRS before them and less comparable to those of “non-adopting” firms that apply domestic standards. Also, adopting firms exhibit increased capital market benefit — liquidity, share turnover, and firm-specific information — relative to adopted and non-adopting firms. There is little evidence of capital market consequences for adopted firms or of non-adopting firms suffering decreased capital market benefits. Our study is motivated by the SEC’s Roadmap for incorporating IFRS into the US financial reporting system. Our findings suggest that permitting US firms to adopt IFRS voluntarily could enhance comparability of US firms’ accounting amounts with those of firms applying IFRS. The findings also support the SEC’s belief that enhanced comparability results in capital market benefits.