Adigeon Prime was an inhabited planet. It was the prime planet in the Adigeon planetary system. This planet was in or near to Federation space. On this planet, the medical establishment performed illegal genetic engineering and DNA resequencing as late as the mid-24th century.
In 2348, seven-year-old Julian Bashir was taken by his parents, Richard and Amsha Bashir, to Adigeon Prime to undergo accelerated critical neural pathway formation. There, the young Bashir's brain was genetically modified, leading to mental and well as physical enhancement. (DS9: "Doctor Bashir, I Presume")
In "Doctor Bashir, I Presume", Bashir recalled seeing many aliens in the hospital on Adigeon Prime, possibly indicating that more than one culture lived on or visited the planet. It may also suggest Adigeon provided these (illegal) services to more than just humans either within or outside the Federation.
The Star Trek: Enterprise novel, The Good That Men Do depicts a visit to Adigeon Prime by Earth Starfleet Commander Charles Tucker in order to undergo surgical alteration. In the novel, the planet is neutral and home to the Adigeons, an avian culture adept at various plastic surgeries and reconstructions. It is said to be located near Romulan territory.