Vaginal agenesis (also known as Müllerian agenesis or Mayer-Rokitansky-Kuster-Hauser syndrome) refers to a condition where there are abnormalities during embryogenesis that cause an underdevelopment of the Müllerian duct. Patients may have complete lack of a vaginal canal and only have a small dimple in that area, or patients may have a foreshortened vagina. Coexistent uterine anomalies (including complete absence of uterus) are often present, although about 5% of patients will have a normal uterus.

The exact etiology of vaginal agenesis is unknown, but it is thought to have genetic components. Incidence is 1 in 5000 women.

Due to the fact that patients will usually develop secondary sex characteristics as expected and have normal growth patterns, despite this being a congenital condition, these patients often will not present until they go without menses at the time of expected menarche (primary amenorrhea). Some patients may present with cyclic abdominal pain related to having a functioning or partially functioning uterus but trapped blood flow due to outlet obstruction.