I was recently in the Atlanta airport, headed for a flight to Tel Aviv, when I noticed something odd: a young man and his 3- or 4-year-old daughter were taken aside and asked to stand behind the security perimeter.

Were they carrying too many toys? Was there something wrong with their tickets? Did they fail the security screening? Could they possibly be terrorists?

None of the above. This gentleman, who was traveling from California to Israel for an important family gathering, had failed to check his passport. The passport hadn’t expired. In fact, it wouldn’t expire for five months and 22 days. But that wasn’t good enough. Like several other countries, Israel will not permit travelers to enter the country unless their passports will remain valid for at least six months after their scheduled departure.

This young father didn’t know the rules. Both he and his daughter were denied boarding, and they had to spend three days in Atlanta getting new documents. The airline kindly waived the customary change fee for rebooking their flights and upgraded them to business class. But, sadly, they missed their family gathering.

What to know about special expiration rules

It’s true: Some countries require that your U.S. passport be valid not only for the duration of your visit, but also for three to six months after your entry or return from their country. This means you have to check your passport expiration date carefully. For example, if your passport expires on March 1, 2007, and you want to travel this coming November, you may need to renew your passport before you go.

Here is a list of some countries that have special passport expiration rules.

Brazil, Ecuador (including the Galapagos Islands), Indonesia, Israel, Malaysia, Paraguay, Romania, Singapore: six months.

Cambodia, Denmark (including Greenland), Fiji, Switzerland: three months (Denmark applies its three-month rule to your stay in any of 15 European countries).

There are many others. Some countries count their expiration windows from date of entry into their country, others from scheduled departure, so be sure to ask. For further information about special passport expiration rules, check the U. S. Department of State’s listing of foreign entry requirements. Other good sources of information are your airline, your travel agent, and the host country’s embassy or consulate.

What to do if your passport will expire in less than six months:

Contact the host country’s embassy or consulate to see if you can get a special visa for travel within the expiration period.

Renew your passport. The State Department says to allow six weeks for renewal, but you can sometimes get it sooner. For example, if you apply during September or December, when relatively few travelers apply for passports, the turnaround time is faster.

Apply for an expedited renewal. For an additional fee of $60, you can get your passport renewed in about two weeks.

Only the U.S. State Department can issue you a U.S. passport. For information on all passport matters, consult the State Department’s Web site.

A few more things you should know about passports:

Many Middle Eastern and African countries will deny entry and refuse to issue a visa if your current passport contains an entry or exit stamp from Israel. If you are in this situation, you should apply for a new passport.

New passport rules are scheduled to take effect for travel to and from the Caribbean, Bermuda, Panama, Mexico and Canada. As of December 31, 2006, a passport or other secure documentation will be required for all travel by air or by sea to or from Canada, Mexico, Central and South America, the Caribbean and Bermuda. As of December 31, 2007, a passport or other secure documentation will also be required for all land border crossings to or from these countries.

If you have been traveling a lot and have run out of passport pages, as I recently did, you can add new passport pages. Be aware that South Africa requires that all travelers have at least two blank pages for visas in their passports.

In most cases, U.S. citizens planning to stay in one country for more than 90 days will be required to provide additional paperwork, such as visas, proof of financial resources, and an outgoing ticket.

Finally, be aware that all U.S. citizens must have their own passport. Children cannot be included on a parent’s passport — even newborn babies must have a passport to travel.

Don’t let your next overseas trip get tripped up by a passport fiasco. Check your passport well in advance, and make sure your paperwork is in order.

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Joel Widzer is an expert on loyalty and frequent flier programs. He is the author of "The Penny Pincher's Passport to Luxury Travel," a guidebook on traveling in high style at budget-friendly prices. E-mail him or visit his Web site.