Within the framework of this paper, first the urban impacts on the existing infrastructure of a megacity, Istanbul is mentioned. Rapid population increase, illegal settlements and illegal urbanisation cause the existing infrastructure to be insufficient. However, great efforts are continuing on completing the infrastructure. Secondly, the probable effects of earthquakes on the existing infrastructure is emphasised based on the extensive experience gained in the last earthquake occurred at Kocaeli. Urgent precautions concerning infrastructure are listed.