The variability of the pollution of roof runoff was investigated considering a variety of possibly influencing factors. Runoff samples were taken from an experimental roof system that allows the comparison of five different roof materials at urban background conditions, and from house roofs at five different locations in the town of Bayreuth, Germany. It was found that local sources (e.g. PAH from heating systems), dissolution of the roof systems' metal components, and background air pollution are the main sources of runoff pollution. Its variability is extremely high in between different roofs (up to three orders of magnitude) and high within as well as in between single precipitation events. The first flush is often heavily polluted and should be treated in an appropriate way. Roofs with metal surfaces should not be connected to infiltration facilities as concentrations of copper and zinc by far exceed various toxicity threshold values.