The 2011 lists of largest professional staffing firms – including largest finance/accounting, legal, clinical/scientific and marketing/creative – are now available to corporate members of Staffing Industry Analysts.

Finance/accounting

Robert Half International Inc. (NYSE: RHI) ranked as the largest finance/accounting staffing firm based on estimated 2010 U.S. finance/accounting staffing revenue of $1.19 billion. It was followed by Adecco SA and Resources Connection Inc. (NASD: RECN).

In total, there were 12 staffing firms with more than $50 million in U.S. finance/accounting revenue.

For the full list of largest U.S. finance/accounting staffing firms, corporate member can click here.

Clinical/scientific

The largest U.S. clinical/scientific staffing firm was Aerotek, part of the Allegis Group, with an estimated $324 million in U.S. clinical/scientific staffing revenue. Kelly Services Inc. (NASD: KELYA) ranked second, and it was followed by inVentiv Health Inc. Thirteen staffing firms had more than $25 million in U.S. clinical/scientific staffing revenue.

For the full list of largest clinical/scientific staffing firms, corporate members can click here.

Legal

Adecco SA ranked as the largest U.S. legal staffing firm with $143 million in U.S. legal staffing revenue in 2010. It was followed by the Hudson Highland Group Inc. (NASD: HHGP). Five staffing firms posted $25 million or more in U.S. legal staffing revenue in 2010.

For the full list of largest legal staffing firms, corporate members can click here.

Marketing/creative

Aquent posted the most U.S. marketing/creative staffing revenue in 2010 of any staffing firm with an estimated $125 million. Three firms generated $25 million or more in U.S. marketing/creative staffing revenue in 2010.

For the full list of largest marketing/creative staffing firms, corporate members can click here.