Tips for traveling with others …

• Start off with a shorter trip, maybe a weekend, to get a sense of your companions’ sleeping and eating schedules and spending habits.

• Talk ahead of time about your plans and expectations. Do you want to stick together for all activities or go off in separate directions?

• If there are children involved, talk about bedtimes, TV watching, and will they accompany adults to all meals and activities or be with sitters?

• Discuss spending habits in case one couple is on a budget and the other has more extravagant expectations.

• Respect each others’ passions and plans: museums or hikes? History or entertainment?

• Make sure everyone has a little personal space each day. You don’t have to be joined at the hip 24/7.

• Don’t take things personally — opinions, moods, food and sleep issues.

Sources: Clinical psychologist Roberta Golden and licensed clinical social worker Jennifer Wand Linnowes.

Call them Missy and Mike and Cathy and Walton’s Worldwide Adventures.

It started unassumingly enough — two couples having dinner to celebrate Dr. Mike Stewart’s 47th birthday in April, 1994. His wife and fellow Sandy Springs orthodontist, Dr. Melisa Rathburn-Stewart, invited along a Buckhead couple who had been mostly Mike’s friends professionally: Dr. Catharine Enright, a pediatric dentist, and her physician husband, Dr. Walton H. Reeves.

Since Mike’s surprise trips and generous gifts to his family and staff are legendary, Missy decided to turn the tables. During the dinner, she presented Mike with a large basket. Inside: a map of the California wine country, cheese and crackers, a corkscrew and a few bottles from the Napa Valley. Oh, and four faux plane tickets that became real boarding passes to California that August.

It was a surprise for their guests as well as Mike. Cathy remembers her reaction: “Sounded great! We were excited and thought it was a very nice invitation.” But Walton remembers: “My initial reaction to the first trip was ‘We can’t afford it.’ Then it was almost embarrassment and shock when Missy said they were treating for most of it as her birthday present to him. And we were not that good of friends, yet.”

It took only one trip to change that. “While the tradition of traveling together began with that first trip,” Missy said, “I never realized how special it would become. … I had no idea at the time that my new friends would become our best friends.”

“We all experienced something magical on that trip,” Mike said.

Thus began two decades of frequent journeys, which will be celebrated during their 50th trip next month.

“We call it better-than-family travel,” said Mike, 67.

On some of the trips, the two couples have included a mix of their seven children on ski, beach and hiking vacations. On their own, they’ve gone farther afield and been more adventurous, taking off for Europe and South America. Still to come will be Scandinavia, Vietnam and fishing in Chile.

Next month, Missy and Mike are going to a conference near Australia’s Great Barrier Reef, where daughter Alexis Stewart, a junior at the University of Virginia studying abroad, will join them. The three then will go on to Sydney to meet Cathy and Walton, and the two couples, minus Alexis, plan to go skiing on the Tasman Glacier in New Zealand.

Though the trips have varied widely, some aspects of them don’t change at all:

• There is always a photo of a circle formed by the right feet of whoever is in the group.

• They enjoy their four- and five-star hotels, but also like to get out, see the people and absorb the history and culture.

• They laugh a lot. “We have so many shared experiences now, no matter where we go we see something that reminds us of a previous experience and start laughing,” Cathy said. “And we cry easily.”

They all claim there is no alpha dog in the group, but the core cast of characters has certain “idiosyncrasies,” Cathy said, “that are all embraced.”

For instance, Mike is keeper of the spreadsheet (they don’t divide checks but take turns picking them up and “true-up” at the end).

Mike has been known to turn around a dire situation — like the time he and Missy missed their flight for a fishing trip in the Pacific Northwest and he chartered a plane to get them to the West Coast. In a typical burst of generosity, they took along a young bridesmaid who had also missed the same flight and dropped her off in Salt Lake City to make her connection in time for the rehearsal dinner.

Missy, 54, and Cathy, 58, do most of the planning. Missy’s stealth research often results in cool, offbeat ideas. Cathy reacts badly to bug bites and usually packs too many shoes.

Walton, 57, is the thrifty one, can shift gears while driving on the wrong side of the road, and is called “Catfish” because he will devour any and all leftovers.

The trips have ranged from guided tours in Spain, Peru and Turkey to self-guided trips across Nova Scotia, England and France. There was a deep-water fishing trip off Florida and more adventurous outings to the Galapagos Islands and Machu Picchu in Peru.

There have been modest accommodations, from the low-budget condo in Colorado they had to clean themselves on arrival and a spartan cinder block house in the Florida Keys, to more posh digs in England, where they traveled for a Van Morrison concert. That journey, their biggest splurge, included a catered dinner in Blenheim Palace and what Walton calls “extravagant nights of sleep” in a nearby English manor house.

Of course, not everything goes perfectly. There have been minor skiing mishaps, Montezuma’s revenge a time or two, a drunken innkeeper at their bare-bones agriturismo in Andalucia, and a peacock that would not let them sleep past dawn.

But, Mike said, “When we settle down to dinner at the end of the day, there is just a huge smile on everyone’s face. We know we have something special and give thanks at every evening meal.”

“I did think twice about inviting the Reeves that first time because I didn’t know them extremely well,” said Missy, the original instigator. “Boy, I sure am glad I went for it! I never realized how special it would become. … Blending our families has been a blessing for all of us.”