Planning a postretirement move from, say, New York to Florida is relatively simple. But if you're thinking about spending your golden years abroad, there are many more unknowns. How can you check out a prospective retirement haven before you make a big move--and maybe a big mistake?

Thanks to books like Retirement Without Borders by Barry Golson and sites like Internationalliving.com, such research is easier than ever. But be careful; much of what you'll find on the Web comes from those with a financial interest in luring you to some locale. Register at some sites and you might be deluged with spam.

Forbes.com is one of a number of online sources ranking foreign retirement havens. Others, such as Mercer (mercer.com/qualityofliving), rate locations worldwide without any special focus on retirement. Read the footnotes: We all have unique ways to weight the different criteria. But lists are only a starting point, and you may be interested in some place that doesn't make them anyway--say, a country you've visited or have ancestors from. Here are some issues to consider and ways to investigate them.

Residency. What's needed legally to become a resident? Many foreign embassies in Washington post clear answers in English. There's a list of links at embassy.org/embassies.

Cost of Living. Ignore those "French living on $30 a day" pitches. They tend to leave off stuff, like medical costs and eating out. What you want is hard, detailed data. Numbeo.com has relative country-by-country breakouts for rent, groceries and restaurants. But remember costs can be lower farther out into the countryside.

Taxation. The U.S. taxes its citizens' income no matter where they live. Those living abroad can claim an annual $91,500 exclusion of income from work, which retirees often don't have. Tax treaties usually protect against double taxation, but many countries have higher rates than the U.S. However, breaks can be found: For example, American expats pay no income tax in France on U.S.-source investments. The Internal Revenue Service's Publication 54 (go to irs.gov) explains the rules for U.S. taxpayers living abroad, while Publication 901 lists the tax treaties.

Health Care. The bad news is that the U.S. government's Medicare program for senior citizens generally doesn't cover care provided abroad. The good news is that in most countries medical services cost far less than they do here. Outfits including the Association of Americans Resident Overseas (aaro.org) and April Medibroker (medibroker.com) offer or broker surprisingly affordable health insurance. But check out the rules on preexisting conditions.

Safety and Stability. The U.S. State Department publishes surprisingly informative "background notes" on 200 countries (state.gov/r/pa/ei/bgn). So does Canada's equivalent (intercultures.ca); search for "country profiles."

Weather. There are endless debates over whose is best. You can use world-climate.com to compare the weather of just about any significant city in the world with what you've been used to all those years. That way you can figure out whether that terrific weather you encountered on your visit (or saw in a brochure) is the norm.

Friendliness/Language. English is not always widely understood abroad nor its speakers appreciated. What's the local temperament? Try using Google ( GOOG - news - people ) Blogs (blogsearch.google.com). Typing "American Expats Uruguay," for example, produces running blogs describing how foreigners fare in that pleasant South American country.

Test Run. Make an extended visit (two months or more) before moving. Rather than the resort that seemed so enchanting, try to rent the kind of housing that might become your home. See how hard it is to register your car or to get the garbage picked up.