Global broker Aon has banked a full-year net income increase of 39% to $US979 million ($910 million), driven by the acquisition of human resources firm Hewitt.

The $US4.9 billion ($4.55 billion) Hewitt deal in 2010 made Aon the largest human resources firm in the world, and provided a 33% increase in total revenue to $US11.3 billion ($10.5 billion) for the full year.

Aon’s full-year results marginally overshot the expectations of analysts, who remain concerned about margins affecting the HR bolt-on.

Net income for the fourth quarter rose 19% to $US277 million ($257 million) on a 3% lift in group revenue to $US3 billion ($2.79 billion).

“Our fourth-quarter results reflect 15% growth in earnings as highlighted by organic growth across all major businesses and the continued delivery of synergy savings related to Aon Hewitt,” CEO Greg Case said.

“While macro-economic conditions remain challenging globally, we are firmly on track to deliver improved growth in 2012.”