Equine coital exanthema (ECE) is a predominantly sexually transmitted disease caused by equid herpesvirus 3 (EHV-3), which is antigenically and pathogenically distinct from other equine alphaherpesviruses. The disease can cause significant economic losses in horse studs which result mainly from the temporary disruption of breeding activities. Infection caused by EHV-3 occurs mostly via direct cutaneous contact during the act of coitus but indirect transmission through contaminated semen or equipment is also possible. ECE is characterized by discomfort and discharge locally and the presence of vesicopustular lesions on the penis, prepuce, vulva and vaginal mucosa and sometimes on the mare’s teats. There is no commercially available vaccine for EHV-3 infection. Treatment of disease is palliative and is directed at aiding natural resolution of the infection and healing of the skin lesions. The aim of this article is to present current data on the prevalence, diagnosis and prevention of this important viral disease of horses.