The two important earthquakes that occurred in Turkey in 1999 have increased concerns on what would happen if a major earthquake affects Istanbul again. Alarming estimates reveal that Istanbul will probably be exposed to a devastating earthquake, with a magnitude between 6.5 and 7.7, in the next 25-30 years. The necessity of comprehensive plans for seismic mitigation, and response and recovery tasks after catastrophic events, has encouraged researchers to develop scientifically advanced tools to conduct loss assessment analyses. After the 1999 earthquakes hit Kocaeli and Duzce, several seismic loss assessment studies were performed for the city of Istanbul; many of them were carried out by the most important academicians in Turkey. However, due to the rapid changes in the exposed inventory of the city, those studies were losing accuracy. This article presents a seismic loss assessment system that can easily reanalyze earthquake scenarios including updates in the exposed inventory. This software can be used by government decision makers and disaster management agencies. In the analysis described in this article, the inventory data for the Zeytinburnu District is updated and visualized by using the rapid visual screening of buildings. Results from a loss assessment for the Zeytinburnu District are presented and compared with results from previous studies. The loss assessment analysis provide estimates of building damage, retrofit cost, economic loss, fiscal impact, and cost-benefit analysis.