For the second time in very recent memory, Aetna (NYSE:AET) raised its guidance today, pushing its stock to a new 52-week high. The health insurance provider has suffered travails over the last several years, and investors apparently took the news as an added sign that things are on the mend.

Aetna said it now expects first-quarter operating earnings of $1.68 to $1.73 per share, as compared to its old guidance for earnings of $1.50 to $1.55 per share. For the fiscal year, Aetna anticipates earnings of $6.60 to $6.75 per share, up from its previous view for earnings of $6.25 to $6.35 per share.

The company associated its improved outlook on increasing membership, moderate medical costs, and better margins.

Aetna was once mighty, but over recent years lost the No. 1 spot to UnitedHealth Group (NYSE:UNH). Other competitors include Cigna (NYSE:CI) and WellPoint Health Networks (NYSE:WLP).

Although the insurance provider suffered a protracted bout of declining membership, lately, it's been pointing to a rising number of members, indicating a possible turnaround. Maybe it's swiping them from UnitedHealth or Cigna, which recently reported dropping membership and troubled times itself.

However, while Aetna grew its earnings when it reported fourth-quarter numbers recently, revenues were still down a few percentage points compared to the same period last year. Aetna shares are currently trading at 13 times forward earnings, using the new guidance. It's been moving steadily higher, having increased about 40% over the last six months, with today's levels the highest since 1999.

Aetna shares were up 5% at one point today. Investors are obviously betting that this is just the beginning of a successful bid to regain dominance. However, with UnitedHealth entrenched and a few years of tough times behind it, it still seems a little soon to call a recovery.

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Alyce Lomax does not own shares of any of the companies mentioned.