Twenty-six pairs of reared apart twins were evaluated ophthalmologically. Included were 18 monozygotic pairs and eight same sex dizygotic pairs. A high concordance of C/D ratios and esotropia was evident. Though reared apart, three pairs of esotropic MZ twins had almost simultaneous onsets of diagnosis and treatment for their strabismus. Genetic influence on the development of refractive errors was evident by the greater similarity of the refractions in MZ twins when compared to DZ twins.