Odour emission of livestock buildings is major burden for ambient residential areas. Using a dispersion model to calculate ambient odour concentrations, the separation distance between livestock buildings and residential areas was defined by a pre-selected odour threshold and an exceeding probability. The dynamic Austrian odour dispersion model (AODM) was used to calculate the separation distance for several combinations of these two values, which represent the protection level of various land use categories. The AODM consists of three modules: (1) odour release on the basis of a simulation model for the indoor climate of livestock buildings; (2) a regulatory dispersion model (Gauss) to calculate hourly or half-hourly ambient odour concentrations; and (3) a fluctuation module, calculating the instantaneous odour concentration, depending on wind velocity and stability of the atmosphere. The calculated separation distances for a pig fattening unit of 1000 heads were compared with empirical guide lines used in some countries (Austria, Germany, Switzerland, The Netherlands, USA). For most guide lines, the separation distances were smaller compared to the model calculation, except for the German guide line applied for non-agricultural areas. Odour sensation occurred predominantly around sunset, with neutral or slightly stable atmospheric stability. The presented AODM is a useful tool for regulatory purpose.