Mid-level vortices are often observed to develop prior to the formation of a tropical cyclone. A numerical modelling simulation of tropical cyclogenesis is carried out which shows the development of a mid-level vortex, and an analysis indicates that sublimation at the base of the stratiform ice layer plays a major role in its formation. Understanding how mid-level vortices form and their role in tropical cyclogenesis may eventually lead to improved forecasts of these major weather events.