The mode of inheritance in the complete cryptophthalmic syndrome is not clear in all cases. In two of our patients with complete cryptophthalmos, one showed a probable autosomal-recessive inheritance, while in the other patient, the mode of transmission could not be determined. Light and electron microscopic studies of the globes demonstrated heterotopic smooth-muscle tissue in the anterior part of the choroid in these two patients. Although these findings might be explained on the basis of a lack of directional growth of the embryonic ciliary muscle cells during the early embryonic period, we favor a simple anatomical explanation based on differentiation arrest of the anterior segment. During the fourth month of gestation, the growing optic cup presumably fails to advance forward normally and to differentiate. The relatively normally developing posterior segment extends posteriorly. The "stretching" backward of the ora serrata during the seventh month of gestation "drags" with it the ciliary smooth muscle that did not advance forward due to the earlier arrest. Thus, in the definite cryptophthalmic eye, the smooth-muscle tissue is localized within the anterior choroid.