Mr. Oh, holding her hand, said, “My dear, I didn’t know that the war would do this to us.”

Ms. Lee and the couple’s son, Oh Jang-gyun, 64, were among 389 South Koreans who crossed the heavily armed border into the North in buses and ambulances on Tuesday to meet with 96 elderly North Koreans who wanted to reunite with long-lost relatives for perhaps the only time. Ms. Lee said that after her husband appeared to her in a dream in 1978, she gave him up for dead and began holding an annual ritual for a deceased relative.

The biggest surprise in her life came after the Koreas agreed in September to hold a new round of family reunions and she heard from the South Korean Red Cross that her husband was alive in the North, looking for her. Since then, she had been busy preparing for their meeting, digging up an old wedding photograph and buying a wristwatch as a gift. The couple’s names are inscribed on the back.

Their time was to be painfully brief. They were granted permission to be together for only 12 hours, in group and private sessions, until Thursday, when they will have to part again. On Thursday, an additional 90 elderly South Koreans will cross the border for another round of three-day reunions with 188 relatives in the North.

The reunions, at the Diamond Mountain resort in southeastern North Korea, are a rare but highly emotional glimpse at the pain the long political divide on the peninsula has inflicted on families separated by the war. For more than six decades, they have been forbidden to exchange letters, phone calls or emails, much less to meet. While their governments have arranged occasional reunions, they have been limited to a couple hundred people. The most recent reunions took place in February of last year.