Regarding non-GAAP measures, reconciliations to the most comparable GAAP measures have also been provided in our most recent 10-K and 10-Q, as well as in the financial supplement.
This call is being recorded and webcast. During the next week, the call may be accessed on CNA's website.
Now I will turn the call over to CNA's Chairman and CEO, Tom Motamed.
Thomas F. Motamed
Thank you, Marie. Good morning, everyone, and thank you for joining us today. Before Craig reviews our first quarter financial results, I would like to share a few highlights.
We are pleased to report improved net operating income of $226 million, up from $213 million in 2011. The improvement in our first quarter results was driven by lower catastrophe losses and strong investment income.
First quarter net income improved to $250 million from $220 million in 2011. Our Specialty business continues to deliver solid underwriting results with a first quarter combined ratio of 97.3%. We are pleased by Specialty's 4% growth, which was driven by improved rate and solid retention, as well as the new to loss business ratio of 1.5:1. Rates in Specialty increased 3% with retention holding steady at 87%.
Specialty hit ratios were down 1% reflecting our continuing focus on selective underwriting, increase in rates and disciplined new business pricing. In fact, new business pricing is stronger than on our renewals.
In Commercial, our first quarter combined ratio was 106.2%, an improvement of nearly 2 points over the prior year period due to lower catastrophe losses. Commercials non-cat accident year loss ratio improved modestly from 2011 full-year results, a reflection of ongoing improvements in both earned rate and risk selection.
Commercial's combined ratio excluding catastrophes and development was 105.4%, up 2.8 points from the prior year period. The unfavorable period-over-period comparison is due to a large insurance receivable recovery in the 2011 period which significantly decreased the expense ratio.