In this work we present results and their analysis of the measurements of the UV Radiation taken in Bogota, Colombia, S.A. The aim was to assess the risk due to solar ultraviolet radiation exposure through ultraviolet index (UVI) during the Nina Phenomenon occurrence and to compare it against another available historical database. The measurements were realized from May 2010 through July 2011 with a spectral radiometer of the series GUV2511 Biospherical Instruments, with three sensor lines in the B-ultraviolet zone, and three in the A-ultraviolet zone. Therefore, in order to evaluate UVI, it was applied the ¨Diffey Dose¨ methodology. It was found a decrease in the monthly mean of ultraviolet solar radiation in Bogota and hence in the same monthly UVIs. However, this fact cannot be interpreted as a decrease of the risk by exposure to UVR in Bogota, because, still persisted very high and extremely high daily UVIs, but with minor frequency. So, in spite of Nina events and high cloudiness in this region, there are both, frequent and extremely high UVI values that represent very high risk to people due to solar ultraviolet radiation exposure.