became the first large national accounting firm to convert from a traditional limited liability partnership, to an entirely employee owned corporation.

Shortly thereafter in 1913, the Sixteenth Amendment to the United States Constitution was ratified, followed by the Revenue Act of 1913 with new impositions of U.S. federal income tax enacted by Congress in that year.

By 1917, Congress enacted the first revenue bills and the U.S. entry into World War I created the need for corporate income and excess profit taxes.

Seidman and his siblings, who joined him in his new accounting firm, seized the opportunity to provide tax services to businesses in addition to individuals.

Fostered by the federal government's conversion of furniture and woodworking companies to aircraft production for the war effort, the firm opened an office in Grand Rapids, Michigan, in 1917.

In 1950, L. William Seidman joined the firm and ultimately became its managing partner before leaving for government service, most notably as chair of the FDIC.

During this timeframe, BDO International was created and has grown to become the fifth largest accounting and consulting network in the world with over 1,591 member firm offices in 162 countries.

In June 2012, the monitor (Joseph A. Smith Jr.) of the National Mortgage Settlement announced he engaged BDO USA, P.C.