This could have been an enormously more difficult effort. I started out with the goal to identify the three best stocks in health care to buy and hold for years, even decades. To come up with a list of the absolute best was daunting. There are just too many variables to say with unwavering conviction that any three stocks are the best to buy and hold.

Identifying great buy-and-hold health-care stocks, though, was much easier. There are plenty to choose from. Here are three that I think meet the mark.

1. Johnson & Johnson (NYSE:JNJ)
Picking Johnson & Johnson was the easiest choice of all. If you look around your house, odds are you'll find several J&J products. If you looked around the hospital nearest to your house, chances are you'd find multiple J&J products there also. What makes J&J a great buy-and-hold investment is that this would have been as likely 20 years ago -- and 20 years from now -- as it is today.

J&J essentially consists of multiple businesses rolled into one. The company is probably best known for its consumer products such as Band-Aids and Listerine. It also claims a large medical devices and diagnostics division. J&J's pharmaceuticals segment developed blockbuster drugs including Remicade and Velcade.

With strong products and continual innovation, Johnson & Johnson saw its stock climb more than 3,100% in the past 30 years and more than 800% in the past 20 years. Along the way, the company not only consistently paid out dividends -- it raised them year in and year out also. If you had reinvested those dividends, by the way, that 30-year return soars to 5,800% and the 20-year return jumps to nearly 1,400%.

2. Express Scripts (NASDAQ:ESRX)
Unlike J&J, Express Scripts doesn't pay a dividend. However, the company's pharmacy benefits management, or PBM, services should remain in demand for years to come. That's especially likely as the baby boomer generation ages and needs more prescription drugs.

There are other PBMs that should prosper also. I like Express Scripts, though, in large part because of its economies of scale as the largest PBM in the nation. That scale should serve as a competitive advantage in coaxing more members to use lower-cost sources like mail-order pharmacies, use cheaper generic drugs, and adhere to prescribed medication regimens.

If you bought the stock 20 years ago and held on, you would now be sitting on gains of almost 12,000%. Yep -- a $10,000 investment in Express Scripts in 1993 would have turned into more than $1.1 million.

3. Gilead Sciences (NASDAQ:GILD)
You might be surprised to see a biotech stock included in the mix of buy-and-hold ideas -- especially one with several drugs losing patent protection in the next few years. I think that Gilead Sciences is one to keep for the long haul, though.

Gilead's gains over the past 20 years rival those of Express Scripts. It currently dominates the HIV/AIDS drug market with products including Atripla, Stribild, Truvada, and Viread. The bad news is that Gilead faces the expiration of patents on some of these drugs over the next decade and increasing threats of competition, particularly from ViiV Healthcare, a partnership formed by GlaxoSmithKline (NYSE:GSK) and Pfizer (NYSE:PFE)

While Glaxo and Pfizer could grab some market share, I think Gilead will maintain its leadership in HIV/AIDS. The company also appears to be poised to be a major player in the lucrative hepatitis C virus, or HCV, market.

Past performance ...
Nearly every financial document you come across will include a familiar phrase along the lines of "past performance is not necessarily indicative of future results." It's absolutely true, of course. Just because any stock performed well in the past doesn't mean they will automatically continue to do well. However, it is reasonable to look at a company's business model and conclude that the probability is pretty good that the model is sustainable into the future.

I wouldn't attempt to predict how much J&J, Express Scripts, and Gilead shares will increase (or decrease) over the next 10 to 20 years. However, I like the business models for these three companies and suspect that they will all be successful over the long run. Buy and hold? You bet.