A study of 260 Jordanians who became blind or visually impaired (according to World Health Organization standards) before the age of 15 years showed the dominant effects of genetically determined causes in two generations. Genetic causes were responsible for the visual impairment in 122 (77.7%) of 157 subjects in the group born after 1970 and for 69 (67%) of 103 in the group born before 1970. There was a statistically significant change in the overall pattern (genetic and acquired causes) of blindness between the two generations, and there was also a significant change in the pattern of acquired blindness alone. A decrease in corneal infections leading to blindness or visual disability in the younger generation was accompanied by an increase of trauma in the same age group. Parental consanguinity in those with genetically determined causes of visual impairment was high compared with those with nongenetic causes (79% vs 33.3%, P < .05). The autosomal recessive mode of inheritance was the most common pattern encountered (53.9%).