The Strait of Istanbul which constitutes one of the major and busiest seaways in the world links the Black Sea to the Sea of Marmara, it is a narrow “S-shaped” channel, open day and night for international shipping. Currents and darkness are the two dominant factors causing marine casualties in the Bosphorus. In this regard, Yenikoy and Umuryeri (or Umur Banki) are the two critical areas where most of the stranding and grounding casualties occur as vessels negotiate sharp turns (80° at Yenikoy, 70° at Umuryeri). The casualty case investigations reveal that in most of the incidents, vessels lose their manoeuvrability in the course of taking a sharp turn with the current. The number of casualties occurring in darkness was found to be nearly twice the number of occurring in daylight. A total of 461 marine casualties of different types occurred in this tricky strip of water during the period 1953–2002, the majority being collisions. Since 1994 when the TSS was introduced there have been 82 marine casualties the majority of which have been groundings/strandings. This paper examines marine casualties in-depth in relation to casualty types, numbers of ships, the localities where most incidents occur, and external factors such as currents and darkness that contribute to marine casualties in the Strait. The major factors are deduced in order to suggest possible solutions.