No case history of conjoined twins can be complete without mention of the Bunker brothers, the original twins from Siam (present-day Thailand). Born on May 11, 1811 in a tiny village along the Mekong river, the brothers were xiphopagus twins, joined by only a small band of cartilage at the sternum. Their livers were fused but were each independently complete. Through practice they were able to stretch the tissue that connected them and stand side-by-side rather than facing one another. This gave the illusion that they were joined at the side, and even today conjoined twins are frequently depicted as joined side-by-side by a sliver of tissue. Separation of Chang and Eng would have been extremely easy, even with 19th century medical technology. Ironically, the boys were three-quarters Chinese and known in their native village as 'The Chinese Twins'.

At age 17, the boys were brought back to America by the showman Abel Coffin, whose associate had initially discovered them in 1824 while they were swimming. In America they toured with P.T. Barnum until their retirement in 1839. They adopted the last name Bunker in 1844, their original Siamese last names having been lost when they joined showbusiness. While in North Carolina, Chang and Eng began to date Adelaide and Sarah Ann (or Sally) Yates, respectively. They were scheduled to marry but locals disapproved strongly of the brothers' courtship of the girls and even threatened them. Fearing for their lives, the brothers arranged for a separation surgery, begging to be separated even if it meant killing them both. However, the sisters intervened just before the operation and married the twins in a quick double-wedding ceremony. One couple purchased a farm adjacent to the brothers' original property and the brothers built separate houses and raised tobacco. From then on, they spent alternating nights with their wives in their own houses and together fathered 22 children (10 were Chang's, 12 were Eng's). However, several of the children died in infancy or early childhood.

In 1874 Chang, the stronger and more stubborn of the twins and a heavy drinker, contracted pneumonia, which was worsened by the carriage trip in the rain between the two farms. He died rather suddenly during the night of January 17. Eng awoke to find his brother dead, and he called for his wife and children to attend to him. According to some stories, the family sent for a doctor to perform an emergency separation, but Eng had died by the time the doctor arrived. By other accounts, Eng refused to be separated from his dead brother. He died three hours later.

The twins' fused liver - the only organ the twins shared - is still preserved in formalin at the Mutter Museum in Philadelphia, Pennsylvania, and is exhibited alongside a plaster death-cast of the twins.