Two patients and 28 others in the literature were ascertained because of congenital vaginal agenesis associated with clinical and/or radiographic evidence of malformations derived from the cervicothoracic somites. In these patients, there was a high incidence of Müllerian duct aplasia/hypoplasia (96%), renal agenesis and/or ectopy (80%), and abnormalities related to cervicothoracic somite dysplasia, particularly 2 to 4 anomalous vertebrae located between C5-T1 (80%). These consistent findings suggest a distinctive non-random association of malformations: Müllerian duct (MU) aplasia, renal (R) aplasia, and cervicothoracic somite (CS) dysplasia (MURCS). Identification of one component of the MURCS association suggests the presence of the other associated anomalies. A hypothesis for the embryogenic pathogenesis of the MURCS association is proposed which attributes the malformations to an alteration of the blastemas of the lower cervical-upper thoracic somites, arm buds, and pronephric ducts, all of which have an intimate spatial relationship at the end of the fourth week of fetal life. A presently unidentified teratogen may be one of the possible causes of the MURCS association on the basis of a lack of familial transmission, normal chromosomal studies, and the similar effects of a known teratogen (thalidomide) on the developing genitourinary tract.