Horse breeders are always interested in the well being of their broodmares as well as the well being of the fetus they are carrying. Advances in reproductive techniques have made it possible to gain insight into how the fetus is progressing as well as the ability to determine its gender. Knowing whether a mare is carrying a colt or a filly can help owners make important decisions concerning their herds and the industry in general. For example, fetal sex determination is used on a regular basis among thoroughbred breeders prior to stock auctions. In this article, we discuss the sorting of equine sperm for sex as well as fetal sex determination via transrectal and transabdominal ultrasound.