One important question to solve is if singular noisy events can affect noise levels in the short, medium, and long term. If the answer is yes and these singular noisy events are present or absent during the monitoring of a place, then long-term noise indices can be overestimating or underestimating, respectively, the noise impact. Therefore, it is necessary to observe and quantify the contribution of these singular noisy events to the annual indices established by the European directive [night level (L_n) and day-evening-night level (L_den)]. As an example of this situation, for a whole year this study quantified in 24 measurement points how some representative sound indices were affected during the FIFA World Cup celebrated in South Africa during summer 2010 in three Spanish cities (Cáceres, Málaga, and Madrid). It is shown how very short singular events lasting only a few hours can alter appreciably the values of annual noise indices.