POYAI, Thailand — Maikaew Panomyai did a little dance coming out of the examination room, switching her hips, waving her fists in the air and crowing, in her limited English: “Everything’s O.K.! Everything’s O.K.!”

Translation: The nurse just told me I do not have cervical cancer, and even the little white spot I had treated three years ago is still gone.

What allowed the nurse to render that reassuring diagnosis was a remarkably simple, brief and inexpensive procedure, one with the potential to do for poor countries what the Pap smear did for rich ones: end cervical cancer’s reign as the No. 1 cancer killer of women. The magic ingredient? Household vinegar.

Every year, more than 250,000 women die of cervical cancer, nearly 85 percent of them in poor and middle-income countries. Decades ago, it killed more American women than any other cancer; now it lags far behind cancers of the lung, breast, colon and skin.