Typical isolated ocular coloboma is a congenital abnormality caused by a defective closure of the embryonic fissure of the optic cup. Although an irregular autosomal dominant mechanism of inheritance has been proposed, there is some evidence of other modes of transmission and etiologies. This report shows an unexpected recurrence of iris coloboma, occurring in three sibships of the same family, that could be explained by a "delayed mutation" or "premutation" mechanism.