On Assignment Inc. on Monday said it acquired a competing company called the Cambridge Group Ltd. for more than $5.5 million.

The Calabasas healthcare staffing company said the deal also includes a two year earn-out provision. Cambridge Group is a privately owned provider of specialized staffing in physician, clinical/scientific, and information technology professionals. It had approximately $11 million in 2009 revenues. It is headquartered in Cambridge, Conn., and has a branch office in Philadelphia.

“This acquisition strengthens our presence in core segments of our business and is expansive to our gross margin,” said Chief Executive Peter Dameris in a press release. “We view this acquisition as an opportunity to expand in some of our fastest growing end markets with very little execution risk.”

On Assignment has 75 offices across the United States, the United Kingdom, Ireland, the Netherlands and Belgium.

Shares were down 16 cents, or 2 percent, to $7.02 in midday trading on the Nasdaq.