A few years ago, Bret Shaw and his girlfriend went backpacking in the wildlands of the Grand Canyon. It seemed quite the romantic getaway. They camped overlooking the Colorado River on a ridge plateau. Nothing above but stars. Nothing underfoot but a silent, poisonous scorpion, which tagged him.

The venom crept up his legs, his torso. Fever and palpitations set in. His vision blurred, he staggered up the trail, where a park ranger presented his options: 'We can radio in a helicopter evacuation, which will cost several thousand dollars, or you can go back to your tent and see what happens.'

Unfortunately, Bret wasn't able to exercise a third option-travel insurance. He didn't have any, like a lot of other adventurous travelers who are good at taking a risk but not as good at calculating the consequences.

Travel insurers, on the other hand, get paid to calibrate those distinctions before you hand over your boarding pass. As grocers of probability, they weigh things, then price them-dengue fever, dismemberment, death, even diarrhea. They know that accidents will happen, whether it's a scorpion bite in Arizona or a bout of appendicitis in Peru. And when they do, it pays to be covered.

A good travel policy can provide immediate access to care, treatment and medication-when you need it, all over the world. It's one less thing to think about on the adventure trail. There's a certain peace of mind that comes from knowing you can quickly be put in touch with someone who speaks your language and can wire money, get you a bail bond or refer you to a doctor or lawyer in a foreign land.

Travel insurance absorbs risk, but as with any investment, there is fine print. Policies vary widely, so start with the basics: Where are you going? What will you be doing? What coverage do you need and what can you live without? How far does your home coverage go? Your credit card, renter's or homeowner's insurance may protect backpacks borrowed by the Hong Kong airport or laptops lifted in Addis Ababa. But that's about it.

Many travel insurance companies were set up by larger underwriters, like Pan-American Life Insurance Co. or Cigna, and are designed to let you pick and choose policies to fill gaps in your current coverage. 'Consumers should take time before leaving to investigate their coverage,' advises Jeanne Salvatore of the New York City-based Insurance Information Institute (III). 'If they are not covered, they can then purchase what they need.'

So what might fit your needs? Rental car insurance in Mexico? Evacuation coverage in Kenya? No problem. You can pick the type of protection you need (trip cancellation, evacuation or referral hot-line service); the extent of the policy (cheap or pricey); and the duration.