Radiation poisoning is the result of overexposure to lethal amounts of radiation. Though symptoms can vary dependent on the person in question, most are fatal.
Daniel Jackson received a massive amount of radiation from stopping a naquadria test from destroying the capital city of Kelowna. The amount of radiation poisoning caused his body to begin bleeding out and resulted in his internal organs to shut down. He only survived by ascending with the help of Oma Desala. (SG1: "Meridian")
Because of inadequate shielding, many of the Genii suffer from smaller amounts of radiation poisoning. Dahlia Radim and eleven others went on a mission as false hostages because they were dying of radiation poisoning. However, Carson Beckett was able to save eight of them, including Dahlia, with experimental treatments. Ladon Radim spared a number of members of the Atlantis expedition in return for saving his sister, and also asked for their help in saving others suffering from similar afflictions.(SGA: "Coup D'etat")
In an alternate reality, a Wraith attempted to contact a hive ship to tell it the location of earth using salvaged parts from his crashed dart. The Wraith had to feed on local humans to stave off radiation poisoning from the equipment. (SGA: "Vegas")