This study deals with probabilistic seismic hazard analysis (PSHA) based on earthquakes that cannot be assigned to specific geologic structures (distributed seismicity). To calculate seismic hazard from distributed seismicity, the PSHA methodology is extended in numerous ways. A simple quantitative seismotectonic model enables statistical incorporation of certain seismotectonic knowledge and the application of attenuation relationships that are based on fault distance. The influence of a large historic earthquake on seismic hazard is taken into account with an energy-based seismic activity rate, obtained by spatial distribution of the released seismic energy. It will be shown that for at least a rough seismic hazard assessment, the type of geometrical seismicity modeling is not a deciding factor. To illustrate this, the classical seismic source zone approach and the improved spatially smoothed seismicity approach are studied in detail to determine their common and distinctive components. Except the geometry of modeling the seismic activity, there is no essential difference between the two approaches. Seismic activity in Slovenia can be treated as distributed seismicity. For this reason, the presented methodology is applied to the calculation of seismic hazard maps of Slovenia as a case study. Manuscript received 22 August 2002.