The US' top law firms grew their headcount by 4% in 2006, according to research that also underlines the dramatic expansion of non-equity partnership in the US.

The results of The National Law Journal's ( NLJ's) annual staff survey, found the US' top 250 law firms employed 121,423 lawyers at the end of September, 4,752 more than at the same period in 2005.

The increase in headcount is marginally down on 2005 when firms grew by 4.4%, but is still a bigger rise than in the previous two years.

Despite only a marginal increase in overall lawyer numbers, partner numbers rose by 5.1% to 48,954.

However, the NLJ survey found that the proportion of salaried partners rose dramatically over the 12-month period, with the number of non-equity partners rising by 16.1%.

The 10 biggest firms in the survey remain the same as last year. They are: Baker & McKenzie with 3,535 lawyers; DLA Piper (3,333); Jones Day (2,167); Latham & Watkins (1,951); Skadden Arps Slate Meagher & Flom (1,915); White & Case (1,907); Sidley Austin (1,712); Greenberg Traurig (1,667); Mayer Brown Rowe & Maw (1,410); and Morgan Lewis & Bockius (1,315).

The survey found that associate starting salaries for the top 10 firms range between $120,000 (£63,000) and $145,000 (£76,000).

The survey also identifies growth disparities between individual practices, with firms such as Orrick Herrington & Sutcliffe and Kirkland & Ellis all swelling their lawyer ranks by more than 100 over the 12-month period.

Cleary Gottlieb Steen & Hamilton corporate partner Richard Lincer commented: "The growth rate is not necessarily reflective. People are not trying to constrain growth, but the figures probably reflect losses to investment banks, which have been recruiting."