This paper presents a theory for the cause of congenital malformations of the heart and other structures associated with absence of the spleen. A colmplete review of the literature and the data of the authors' 5 cases lead to this proposal: a lethal factor, possibly the product of a faulty ovulation, specifically affects the germinal bed of the mesoblastic surface of the coelom at an ovulatory age of 24 to 28 days.