Acute vulvar ulcer or ulcer of Lipschutz corresponds to a rare disease, being usually underdiagnosed. It is characterized by a sudden or acute development of ulcerous and painful lesions in the vulva, vagina and/or perineum, without a previous history of sexual contact in girls and teenagers. Its etiology remains unknown in most cases, although they have been associated with infectious agents. Their study includes the suspicion of sexually transmitted infections, adverse drug reactions, autoimmune diseases and immunosuppression. The ulcerative lesions disappear spontaneously, usually without sequelae or recurrences in the long term. We present the case of an 11-year-old adolescent patient, without sexual initiation, or menarche and who consulted due to a four-day prodromal condition, followed by the acute development of genital ulcers. Its causes, clinical presentation, differential diagnosis and treatment are discussed.