The inheritance of congenital miosis in 2 pedigrees is described. The inheritance was autosomal dominant in one and autosomal recessive in the other. The pupils were 0.5-2.5 mm diameter, reacted normally to light and accommodation but dilated poorly with mydriatics. In both pedigrees, the affected members had enlarged corneas. The five members in the autosomal dominant family were myopic and had translucent peripheral irides. Iridodonesis was presented in both members of the autosomal recessive pedigree. The embryology and innervation of the iris muscles together with the ocular abnormalities and syndromes associated with congenital miosis are reviewed.