Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between different classes of disease that involve visual image degradation and astigmatism. Control data comprised refractions from 79 normal vision children. Children were classified into groups according to the category of disease (14 groups) and the reported age-of-onset of their visual disability (0 to 13 years, 5 groups). The mean astigmatism for all groups of children with low vision was larger than that of the normals and in most cases the difference was significant at the 95% level. Astigmatism was highest in children with albinism, retinitis pigmentosa, and idiopathic nystagmus. Increased prevalence of astigmatism compared to normals was noted in children having their onset of low vision as late as 13 years of age. In the low vision subjects with-the-rule astigmatism occurred more frequently than oblique or against-the-rule astigmatism and oblique astigmatism more frequently than against-the-rule astigmatism.