Theoretical discussions of internal organization stress the importance of organization for firm success and profitability. The Williamsonian hypothesis that firms organized using M-form should be more profitable than firms organized using U-form or other organizational structures is the focus of empirical testing in this paper. Pairs of firms are observed over two periods of time. In the first period, the principal firm adopts M-form while the control firm is organized with a non-M-form structure. In the second period, the control firm adopts the M-form structure. Using this matched firm technique across a number of industries, we find the adoption of M-form leads to statistically significant increases in return on asset and return on equity measures.