The Colombian population is exposed to extreme UVR all year round. Colombia, located at the northwest of South America, between latitudes 12oN and 4oS, has extreme levels of UVR during 365 days a year. The UV levels of the 12 largest cities of Colombia are presented, as well as the experimental measurements taken at the city of Medellin (Altitude: 1,470 m, Latitude: 7oN, Population: 2,000,000). The UV Index normally reaches high about 9 points: the extreme category according to the internationally established UV Index scale