Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the health-care industry to thrive over time as our world population grows, ages, and needs medical help, the iShares Dow Jones US Healthcare ETF (NYSE: IYH) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.47%.

This ETF has performed rather well, beating the world market handily over the past three, five, and 10 years. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a low turnover rate of 7%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Plenty of health-care companies had strong performances over the past year. Alexion Pharmaceuticals (Nasdaq: ALXN), for example, spiked 93%, expanding its pipeline by purchasing some smaller biotech companies and enjoying revenue from sales of Soliris, an approved drug for a rare blood disorder. (Many biotech companies have a lot of promise, but no treatments actually approved and selling.)

Intuitive Surgical (Nasdaq: ISRG) gained 18%, continuing to sell its robotic surgical machines to hospitals and to secure valuable recurring revenue from them via service contracts and sales of accessories and supplies. Its growth has slowed, but it's still boosting revenue and earnings by more than 20% annually in recent years. The stock took a hit recently on concerns about a pullback in prostatectomy procedures and its impact on overall growth. But my colleague Brian Orelli has explained that hysterectomies are "the new rocket ship" -- and sees the stock drop as a promising buying opportunity. Some Fools think this company is one of the greatest businesses around.

Abbott Labs (NYSE: ABT), up 30%, is on the verge of big change, as it splits itself into two companies. It has been different from many big pharma outfits as it was also a major player in nutritional medicines and medical devices. Bears worry about patent protection expirations for some drugs, and competition for others, such as rheumatoid arthritis treatment Humira. Abbott has been raking in billions from emerging markets, but warns about currency conversion effects and cyclicality there.

Celgene (Nasdaq: CELG) rose 13%, recently posting promising results for an anti-inflammatory drug. Some are watching to see how smart a move it is for the company to shift its focus from narrower-niche cancer drugs to broader diseases that feature more pharmaceutical competition.

The big picture
Demand for health-care products isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

The health-care market may be huge, but Fool analysts see another huge market in the making. Learn how to profit from it in our free report "The Next Trillion-Dollar Revolution." Get your free copy by clicking here.

Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter, owns shares of Intuitive Surgical, but she holds no other position in any company mentioned. Click here to see her holdings and a short bio. The Motley Fool owns shares of Abbott Labs and Intuitive Surgical. Motley Fool newsletter services have recommended buying shares of Intuitive Surgical. The Motley Fool has a disclosure policy.

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