The distribution of air pollutant concentrations around buildings is a main concern of building and air-conditioning engineers that design the ventilation inlets and outlets on building facades or roofs. CFD is increasingly used to predict air flow and related processes around buildings. In this paper, the possibilities and limitations of CFD for simulating air pollutant dispersion around buildings are discussed. The focus is on dispersion around an isolated building, as the generic basic case for dispersion in the urban environment. The advantages and disadvantages of RANS and LES are briefly described, and results from three different cases obtained in separate studies are compared and discussed. It is shown that even for the case of an isolated building, considerable difficulties exist and that CFD is not yet at a stage where it can be used as a stand-alone practical engineering tool for pollutant dispersion modeling.