This paper focuses on the application of a simple analytical parameterization to the filling of the Ultraviolet Index (UVI) data gaps, and the reconstruction of past UVI values at Badajoz and Caceres (Southwestern Spain). The empirical model involves three independent variables: the solar zenith angle, the total ozone column and the clearness index. Regarding the first application, daily UVI was estimated for more than 30 days when UV measurements were not available in 2007. For these cases, the missing UVI data were replaced by estimated values, thus affecting the UVI annual mean and median. Regarding the second application, the reconstruction of past UVI time-series (1950–2000) is performed only for clear-sky cases (cloud and aerosol free conditions) using the COST 726 total ozone climatology. The linear UVI trends for two periods (1957–1978 and 1979–2000) are calculated for summer months using linear least squares fits. Both locations show statistically significant UVI trends for the most recent period 1979–2000, with values of +4.4 ± 1.6% per decade for Badajoz, and +4.9 ± 1.8% per decade for Caceres. This result is mainly driven by the ozone decline at northern mid-latitudes during this period. No significant trend is found for the other analysed period.