Vaginitis is a rare disease in adult female dogs. However, knowledge regarding this illness is important because, if secondary to reproductive tract anomalies that go uncorrected, it can cause ascending uterine infections and, consequently, subfertility or even infertility. Usually, these infections are caused by Enterobacter or microorganisms from the urogenital inferior system, such as Staphylococcus spp, Streptococcus spp, Escherichia coli, Proteus spp, Pseudomonas aeruginosa, Pasteurella, etc. In some cases, vaginitis may be caused by primary infections with Brucella canis, which is zoonotic, or by canine herpesvirus; both of these agents have the potential to cause reproductive failure. The disease can occur in any age, breed or ovarian condition and can be identified by vaginal cytology, vaginoscopy and culture of vaginal secretions. The most common clinical signs are erythema of the vaginal mucous, vaginal discharge, pollakiuria, licking of the vulva and attraction of male dogs, independent of the phase of the estrous cycle. This disease is generally self-limiting, and the treatment, when necessary, consists of antibiotic therapy, vaginal cleaning with antiseptic and, eventually, surgical correction of predisposing abnormalities.