Excessive exposure to ultraviolet (UV) radiation may bring about health effects on human body, including sunburn, wrinkling and increased risk of skin cancers and cataracts. The Ultraviolet Index (UVI) is a measure of the intensity of UV radiation relevant to the effect on human body (World Health Organization, 2002). To raise the public awareness of the potential harm of UV radiation, the Hong Kong Observatory (HKO) started a UVI advisory service in 1999 to provide information on measured UV radiation to the public (Leung, 2003). In 2006, the HKO launched a UVI forecasting service which enabled members of the public to plan protective measures against possible harm from UV radiation (Lee, 2007; Wong, 2008). The UVI observation and forecast information was disseminated to the public through various channels. This article documents the method and statistical analysis of the UVI measurement, the development of the UVI forecast technique and its performance, and the various UV-related services provided to the public by the HKO.