Background/aim: COVID-19 has now become a global pandemic. Understanding the routes of transmission is vital in the mitigation and suppression of the disease. Istanbul has become one of the disease's epicenters. This study aims to describe the first COVID-19 case and contact tracing efforts around it in Istanbul. Materials and methods: The descriptive study was conducted in Istanbul, Turkey. The first COVID-19 cases and those associated with them were investigated with contact tracing, and primary and secondary cases were described. Results: The source case was an individual who returned to Turkey from international travel at the beginning of March and tested PCR (-). The index case is the brother of the source case and is considered the first PCR (+) case diagnosed in Istanbul. Contact tracing revealed 23 PCR (+) cases, 14 of which resulted in hospitalization and three deaths. Conclusions: This study described cases of the first COVID-19 cluster in Istanbul. Moreover, contact tracing was used in this first cluster. This contributed to contact tracing algorithms in Turkey.