PIEDMONT, S.D. — In 1982 when Deb Ohm got a Christmas card from her brother, Rick McGrath, it came equipped with a big surprise: the same card she had sent him the year before, complete with her original well-wishes.

“I was like, ‘What is this? I don’t get it,”’ Ohm said. “Then it dawned on me, and I just thought, ‘Oh my gosh,’ and it became a regular thing.”

Ohm, 52, of Plainview, and McGrath, 56, of Piedmont, have sent the same card back and forth for 35 Christmases, always with a brief message and the date; 2015 was McGrath’s year to be the recipient.

“It’s a little beaten-up now,” McGrath said, “just like the two of us.”

The card is in relatively good shape for a 35-year-old piece of barely thickened paper. The connecting fold has worn completely through, so the two sides are held together with tape. Its original message, “I couldn’t let Christmas go by without sending something,” is still legible.

It started as a simple way to say “Merry Christmas” from Ohm to McGrath, who was stationed at Myrtle Beach Air Force Base in South Carolina in 1981, when he was 22, his sister 18.

“We sent him a care package, and in the card I sent him a small version of my senior class picture,” Ohm said. “I told him he’d get the bigger picture when he got home.”

McGrath, however, has a bit of a practical joker side, and he decided to send her the card back the next year.

“She never expected it, but I knew she’d get a kick out of it,” McGrath said.

The card has bounced between the two ever since, following McGrath to Korea when he was stationed there from 1983 to 1985 and 1989 to 1991 and now to South Dakota, where he also was stationed in 1991.

He joined in the Air Force in 1978. When he first received the card, he was an airman first class, one of the lower enlisted designations; by the time he retired, his sister was addressing the card to Senior Master Sergeant McGrath, nearly at the top of the career ladder.

Ohm said they worry about forgetting to send it back, or an even worse fate.

“I always think, ‘Is it my year to send it?’ but I always have it on the odd years,” Ohm said. “We always joke that at some point one of us will lose it, or it’ll get lost in the mail, but so far we’ve been lucky.”

The card has gone beyond a two-person tradition to become something their family members ask about.

“Every year, ‘Where’s the card? Did you get it yet?”’ Ohm said.

They plan to keep going as long as they can.

“It’s something special for us,” Ohm said. “Something that the two of us have in common.”

“I would imagine,” McGrath said, “we’ll keep it up until one of us goes to the other side.”