In a survey of 26,512 children under 12 years of age, 2 cases (0.075%) were found to have congenital intraocular coloboma. Among 193 cases of the disease from 169 families reported by 50 hospitals of 21 provinces and cities, the disease affected boys more than girls. Bilateral colobomas of the uveal tract constituted majority of the cases, and the unilateral patients showed no predilection for either eye. The colobomas mostly occurred in the lower part of the eye, involving one or more tissues, depending on the shape, scope and location of the coloboma and whether other ocular deformities existed. Colobomas of the uvea, optic nerve and macula lutea were mostly sporadic. Earlier disruptions in the embryonal cleft resulted in more serious colobomas and complicating ocular deformities.