If you want to see my eyes start rolling in separate orbits, just ask me how I managed to miss picking up UnitedHealth (NYSE:UNH) in 2000. After all, I was a health-care analyst! Since then, the stock is up "only" a bit more than 400%.

A key part of the UnitedHealth strategy over time has been the acquisition of other companies -- and it's at it again. On Wednesday, it announced an agreement to acquire PacifiCare Health Systems (NYSE:PHS) for $8.1 billion in stock and cash. Provided that the deal goes through, PacifiCare owners will get 1.1 shares of UnitedHealth stock and $21.50 in cash.

This will be an interesting acquisition for UnitedHealth -- buttressing the company's efforts in the West/Southwest and in Medicare. Because it's more focused on senior care than most other managed-care providers, PacifiCare gets about 40% of its revenue from Medicare programs.

This deal would also expand UnitedHealth's operations in California. To me, that's a decidedly good-news, bad-news sort of situation. True, California is a huge market and rates in the state have been catching up of late. But California can also be a bit "quirky" with state ballot propositions, and there's no telling whether or not a popular vote in any given year could ratchet up costs or regulatory burdens for managed-care providers.

What's more, the California insurance commissioner has already taken the stage and promised "close scrutiny" of the deal. Back a bit, when WellPoint (NYSE:WLP) was buying Anthem, the commissioner was able to wrangle concessions from WellPoint in exchange for vetting the deal. So, while the commissioner probably won't block this deal, UnitedHealth will likely have to kiss the ring and be willing to make at least some concessions.

All in all, this will likely prove a successful move for UnitedHealth. Though there are some risks from even greater exposure to government and commercial underwriting, there will be cost synergies and UnitedHealth's increased size should give it even more leverage with hospitals, as well as drug and device makers.

So, does anybody lose? I'd say it certainly turns up the pressure on the likes of WellPoint, Aetna (NYSE:AET), and CIGNA (NYSE:CI) to keep a competitive scale of business (though WellPoint will still be the largest, even after this deal). It could also pressure smaller players like WellChoice (NYSE:WC) or Health Net (NYSE:HNT) to accept a buyout deal, rather than continuing to compete against ever-growing giants.

It could also be bad news down the road for Medco (NYSE:MHS) if UnitedHealth were to decide someday to switch its pharmacy benefits management business to PacifiCare's captive operations. That said, Medco and UnitedHealth have a contract in place, and UnitedHealth publicly reaffirmed its commitment to stick with Medco.

For now, though, this is a story of the big getting bigger and, hopefully, better. UnitedHealth may be upping its operating risk a bit, but that could also spell greater rewards down the line.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).