We report experimental and theoretical investigations of the Hall effect in YbRh2 Si2 and its reference compounds LuRh2 Si2 and YbIr2 Si2. Based on band-structure calculations we identify two bands dominating the Hall coefficient in all these compounds. For the case of LuRh2 Si2 -the nonmagnetic reference compound of YbRh2 Si2 -the temperature dependence of the Hall coefficient is described quantitatively to arise from two holelike bands. For YbIr2 Si2 and YbRh2 Si2, renormalized band calculations yield two bands of opposite character. In YbRh2 Si2 these two bands almost compensate each other. We present strong indications that sample dependences of the low-temperature Hall coefficient observed for YbRh2 Si2 arise from slight variations in the relative scattering rates of the two bands. Minute changes in the composition appear to be the origin. The results of our band-structure calculations reveal that a transition of the 4f electrons from localized to itinerant leads to a decrease in the Hall coefficient. © 2010 The American Physical Society.