First-quarter net income rose 56.7% at Administaff Inc. (NYSE: ASF) to $13.2 million, compared with $8.4 million in the first quarter of the previous year.

The Houston-based professional employer organization said gross profit rose 27.2% as the average number of worksite employees increased 8.3% and the average gross profit per worksite employee rose to $254 per month from $216 in the first quarter of 2007. A higher-than-expected surplus from payroll taxes helped boost results.

Gross margin rose to 19.0% from 16.7%.

First-quarter revenue increased 11.8% to $456.1 million from $407.8 million in the first quarter of 2007.

Administaff also announced that it acquired USDatalink, a Baytown TX-based provider of pre-employment background checks. USDatalink provides checks on criminal records, employment history, education, driving records, credit, and more. Terms of the deal were not announced.

Administaff Chairman and CEO Paul Sarvadi said the deal will provide cost savings to its PEO business and expand its human resources service offerings.

Administaff Inc. (NYSE: ASF)
For the first quarter ended March 31, 2008, compared with the same period in 2007.
Revenue: $456.1 million, +11.8%
Net income: $13.2 million, +56.7%