The vulva functions as the most caudal of the three physical barriers between the uterine lumen and the outside world. A compromised vulval seal predisposes to pneumovagina (wind sucking) in mares and may lead to inflammation and ascending contamination of the caudal reproductive tract with pathogens, and/or urine pooling in the vagina. Abnormalities of a mare's perineal conformation and an inadequate vulval seal are most often corrected using Caslick's operation, a procedure that involves surgical apposition of the dorsal part of the vulval labia. The reasons for poor vulval conformation, and therefore the indications for a ‘Caslick's’, vary but can include advanced age, trauma induced by foaling, weight loss and, in some breeds, congenital predisposition. If Caslick's operation is insufficient to resolve the pneumovagina more invasive surgical procedures, such as vestibuloplasty or perineoplasty, should be considered.