An unusual case of left internal thoracic artery (ITA) origin from the thyrocervical trunk (TCT) was detected during routine cadaver dissection. The variability of origin and course of ITA has less or more frequently been documented in the literature. However, the ITA origin from the TCT on the left side has been detected less commonly, making its dissection and preparation during coronary artery bypass grafting surgery more difficult. We discuss the ITA origin and course variability as well as clinical significance of the present variant, reviewing the relative literature. The objective of our study is to exhibit a rare ITA origin in order to provide a more accurate knowledge of such variations.