Uncertainty in total ozone column (TOC) values is quantified for eight different databases through a direct comparison with ground-based data at three Spanish locations, the maximum uncertainty being about 10.5 DU. A long-term TOC series is constructed using the mentioned databases from 1950 to 2011 for nine locations in the Iberian Peninsula. The monthly TOC climatology in the nine locations is presented. An exhaustive analysis is performed of TOC series trends and their statistical significance in the periods 1950-2011, 1950-1984, and 1985-2011. A significant ozone reduction between 1950 and 2011 appears in the Iberian Peninsula with a strong reduction from the late 1970s to the mid 1990s and with more or less constant or slightly increasing levels in the last 17 year. These trends are recalculated taking into account of uncertainty in the TOC values of the series, with a decrease in the number of statistically significant trends emerging. The statistically significant trends in annual and in the averaged Iberian Peninsula series are usually still significant even considering the uncertainty. Finally, a study is carried out of the uncertainty caused by TOC uncertainty in total shortwave (SW) and erythemal ultraviolet (UVER) irradiances simulated under cloudless skies using a radiative transfer model.