We investigate the relationship between the effective tax rate (E.T.R.) and company size in Germany to test tax planning-political power versus political cost theories. In contrast to most studies in this field, which use linear approximations, this paper uses a quantile regression approach. We use data from Compustat, corresponding to non-financial listed companies during 1992-2009. The results indicate a nonlinear relation, with a positive sign for the first quantiles and a negative one in the last part of the distribution. Additionally, leverage, inventory intensity and return on assets are found to be significant determinants of the E.T.R.