We report the familial occurrence of diaphragmatic agenesis in association with other midline anomalies in a brother and sister. Opitz and Gilbert [Am J Med Genet 1982, 12:443-455] introduced the concept of the midline as a developmental field, and there have been reports of pedigrees compatible with the hypothesis of an X-linked gene regulating the development of the midline. This family suggests that an autosomal gene also contributes to the morphogenesis of midline structures.