The aim of this study was to assess the exposure and potential effects of the toxic elements released by the Aznalcollar spillage on the fecundity of the booted eagle (Hieraetus pennatus) population of Doñana National Park. As, Cd, Cu, Pb, Zn, Sb and Tl levels were measured in the blood of 24 individuals after the accident and also used data of reproductive performance of the species from 1976 to 2000. These levels were higher in adults, but they did not differ significantly between age classes and were at safe levels. In addition, a positive relationship between relative fecundity and the combination of Cu, Zn and Pb was observed. Following the mining spill, the mean population fecundity was lower than before. However, the decrease in fecundity over time was also related to the increase of breeding pairs, suggesting a density-dependent regulation and nullifying the mining spillage effect. Thus, although raptors have proved to be highly valuable biomonitors of environmental pollution, we must be especially cautious and go beyond the apparent effects that sometimes we quickly believe to detect, leading us to reach mistaken conclusions that could affect our management plans. informacion[at]ebd.csic.es: Gil-Jiménez et al (2017) The role of density-dependence regulation in the misleading effect of the Aznalcollar mining spill on the booted eagle fecundity. Sci Total Environ http://dx.doi.org/10.1016/j.scitotenv.2017.01.098