On Friday, Cigna (NYSE:CI) reported Q3 results that reflected strong year-over-year growth. Yet investors were apparently spooked by negative margin trends in the insurer's health-care and disability/life insurance segments, as well as an outlook for 2008 that was below Wall Street's expectations.

With shares closing down 3.5% on Friday, I would view this as a buying opportunity for investors looking for more stable investments for their portfolio, given the market's recent volatility. Despite the fact that shares are up about 24% in the past 12 months, Cigna's management still feels the company is undervalued, as seen in the $235 million repurchase of its shares in the third quarter.

Share repurchases persist among the large-cap health insurance companies, with WellPoint (NYSE:WLP) repurchasing $2.4 billion worth of its common shares in its Q3. UnitedHealth Group (NYSE:UNH) bought back $2 billion worth of shares during the quarter, and Aetna (NYSE:AET) recently announced $1.25 billion in planned share repurchases.

Cigna's Q3 adjusted operating EPS improved by 37% on a 7% increase in revenue compared with its year-ago quarter. Rate increases as well as growth in medical membership were the big factors.     

One concern for shareholders would be the decline of 40 basis points in margins (segment earnings divided by segment revenues) that occurred both in the health-care segment and the disability/life insurance segment. With that said, management's forecast of about 5% growth in adjusted operating earnings per share for 2008 seems to be not only attainable, but also an attempt to manage Wall Street's expectations. 

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Fool contributor Billy Fisher has no financial interest in any stocks mentioned. The Fool has a disclosure policy.