Warren Buffett is no fan of short-term trends. Rather than focusing on the flavor of the minute, Buffett instead fixates on trends that will last decades.

And then he makes a fortune off of them.

Take his investment in Coca-Cola (NYSE: KO), for example. Buffett began buying the soda maker in 1988, eventually acquiring about 7% of the company, thinking it had room to grow in the developing world.

He was right. What was a roughly $1 billion investment for about 200 million shares is now worth nearly $14 billion.

But it doesn’t stop there. The same can be said for his stakes in Wells Fargo (NYSE: WFC), American Express (NYSE: AXP), IBM (NYSE: IBM), the list goes on…

Buffett’s stock purchases are some of the best examples of what we call “Forever Stocks.” It’s a term coined by Paul Tracy, StreetAuthority’s co-founder and chief investment strategist of our Top-10 Stocks newsletter. Forever Stocks are stable, growing companies you buy and hold almost quite literally “forever.” And like Buffett’s Coca-Cola stake, you can make incredible gains over time, while resting easy knowing that you own shares of a solid company.

Back in February, I briefly mentioned that the billionaire investor’s firm, Berkshire Hathaway (NYSE: BRK-A) (NYSE: BRK-B), had acquired more than $200 million worth of stock in another company, one of the leading kidney dialysis center operators in the United States.

So did Buffett just buy another Forever Stock?

I think so. Here’s why…

The stock Buffett bought is DaVita (NYSE: DVA). And as I said, the company provides dialysis treatment to patients with kidney failure, also known as end-stage renal disease.

The loss of kidney function is usually irreversible and requires dialysis to remove toxins, fluids and salts from the blood — functions that the kidney would usually perform. Kidney failure is caused by ailments such as diabetes, high blood pressure and other less common kidney diseases. Diabetes continues to grow into an epidemic in the United States, due an aging population and unhealthy eating habits. (Older Americans are much more susceptible to higher blood pressure and other kidney ailments as they continue to age, and I don’t have to tell you the staggering statistics behind the obesity problem plaguing this country.)

This is obviously not something that’s appealing for the health of individuals, but it is driving DaVita’s growing business. During the past three years, DaVita has grown annual sales by more than 7%, up to a recent $7 billion, and profits have grown a very respectable 12% each year, up to $2.3 billion. Going forward, this trend is highly likely to continue — the first wave of Baby Boomers just reached 65 years old last year.

DaVita ran 1,820 dialysis centers in the United States at the end of 2011. This was up 33% from just over 1,300 centers in 2007. Underlying demand is growing and steady, as there are few options other than dialysis for many of these ailments. Kidney transplants are an option, but it can take many months and even years for a donor match to become available, to say nothing of the cost.

As you might imagine, the business is stable and very profitable. Last year, DaVita generated just close to $800 million in free cash flow, or about $8.08 per diluted share. As a reminder, free cash flow is capital left over after a company has paid for its regular business operations and invested in growth. That $8 per share cash flow figure I just mentioned is pretty impressive, as it’s nearly 10% of DaVita’s share price (the stock currently trades for about $86 a share). This left room for the company to buy back more than $300 million of its own stock and acquire additional dialysis centers.

Combined with the fact it is growing, it is easy to see why Buffett would want to own this stock.

Since the time Berkshire made the purchase, the stock has rallied only about 2%. It has, however, rallied close to 16% so far this year, while the market has also had a strong 12% rally.

That’s nice, but I don’t think this matters much. As I said, I think Buffett just bought a Forever Stock — one that will likely deliver staggering results over the long-term. It’s a lot easier to sleep at night, not worrying about the short-term fluctuations, knowing you own a well-run company riding a mega-trend like this one.

I would say that DaVita will outperform archrivals as well, but there simply aren’t may direct rivals in the United States. Fresenius Medical Care (NYSE: FMS) is in the same line of business and, along with DaVita, controls roughly 32% of the domestic market. But Fresenius is based in Germany and operates in more than 40 countries. It is also valued much more richly than DaVita, with a forward price-to-earnings (P/E) ratio of 18. DaVita, meanwhile, trades at a more compelling P/E of 14 and has been growing much faster.

Risks to Consider: Medicaid accounts for close to half of DaVita’s sales. Government programs are notoriously unpredictable and stingy, but so far, DaVita has had little problem negotiating profitable, though low-margin, reimbursement levels from Medicaid. And again, patients have few other treatment options.

Action to Take –> Buffett has a reputation for being one of the most loyal stockholders in history. And given its stable and growing revenue streams, it seems hard to go wrong for investors willing to hold DaVita for the long haul. By my reckoning, it’s a true Forever Stock.

[Note: If you’re wondering who coined the term “Forever Stock,” that would be none other than StreetAuthority co-founder Paul Tracy. He’s put together a special report, called “Top 10 Stocks to Hold Forever,” in which he describes what makes a stock worth holding forever and gives the names of some of his favorites. Go here to learn more.]