Henry Khunrath Pancoast was born on February 26, 1875, Philadelphia, Pennsylvania, United States. He was the second son and youngest of three children of Doctor Seth Pancoast by his second wife, Susan George Osborn. He had three older half-sisters and, by his father's third marriage, a younger half-brother and a half-sister. The elder Pancoast was a professor of anatomy in the Pennsylvania Medical College. Of an occult turn of mind, he discussed in his book Blue and Red Light: or, Light and Its Rays as Medicine (1877) the use of rays, electricity, magnetism, and the effect of filters in the use of the various wave-lengths of light in the cure of disease, a curious foreshadowing of his son's later work.