I HADN’T SPOKEN TO MY COUSIN DENISE IN DECADES. We weren’t even Facebook friends. Now here we were, both in Boston, both prepped for surgery, and about to become about as close as any two people could be.

My mind went back to the late ‘60s, when we spent the long, hot days of our family vacations playing endless games of freeze tag. When it rained, we’d set up tournaments for Parcheesi and Go Fish. My brothers would fuss about having to turn in, but bedtime was my favorite part of the day. I got to sleep in the room with Denise and her sister, Eva, and gab into the night with the sisters I never had.

Life carried us off in different directions. Our parents stayed in touch, but Denise and I drifted. I ended up in Atlanta, she was in Massachusetts. I heard through my mom that Denise—my mom always called her “my little bag of peanuts”—had some rough times. She’d developed celiac disease when she was in her 30s. Before my mom died of cancer, she asked me to look in on Denise, and look after her if I could.

By the spring of 2014, Denise had developed polycystic kidney disease and needed a transplant. Her husband wanted to donate his kidney. He was deemed a match, and everything was a go until his doctors discovered arteriolosclerosis on the artery leading to his kidney. The procedure would be a risk to his health. A new donor had to be found, and the clock was ticking.

I never imagined myself as an organ donor. Needles, well, I just need to see one to start getting dizzy. For a while I thought surely someone else—someone more qualified than I was—would step forward to be a donor. But no one did.

So here we were somehow, in the waiting room, getting ready for surgery where we both would be facing a heck of a lot more than needles. After 34 years of not seeing each other, it had been a pretty intense few months. Medically, there was test after test—blood type compatibility, tissue antigen compatibility—and what seemed like hundreds of screening questions.

But Denise and I also had three decades of important things to catch up on—the grown-up version of our pillow talk. It wasn’t long until I discovered my sister again. Turns out we had faced similar heartaches and shared some of the same joys. We both received teaching degrees, married, had children, juggled careers and experienced the loss of our mothers. If I had met Denise on the street today as a total stranger, I would have loved her.

Denise said goodbye as they wheeled me into the transplant department. With a tight hug, she whispered, “There are no words good enough to thank you for giving me your kidney.” I hugged her back and said, “Well, I really wasn’t sure what I was gonna do with that extra kidney anyway.” We laughed and then I heard my name called. It was time.

While I’d had nightmares about how scary surgery would be, the mood in the room was almost joyful. One nurse was particularly encouraging. Turned out he was in the kidney donor club too. “I’ll show you my scar, if you show me yours,” he joked. Everyone who helped me get ready had something sweet to say. It was almost like giving birth (minus, of course, the contractions). And as much as I had worried about the pain, as they connected me to wires and gizmos, I drifted into a peaceful, deep sleep.

When I woke up, my first reaction was panic. I was certain the transplant hadn’t taken place and that something was wrong with Denise. But the nurses who surrounded me had nothing but good news: The procedure was successful. Denise was fine. Her brand-new kidney—my kidney—was already working.

Denise and I celebrated our transplantaversary together in Boston last December. We’re both doing fine. We talk all the time now, and we made a pact to take care of each other for the rest of our lives. I didn’t lose a kidney, I gained a sister.