Background: There are relatively few studies on causes of childhood visual impairment. This study determines causes of visual impairment and resultant visual acuity among students enrolled at the Alabama School for the Blind (ASB). Methods: All students enrolled at ASB during the 1996-1997 school year (N = 123) were examined between April 1994 and March 1997. A retrospective record review was performed to determine the primary cause of visual impairment and the visual acuity with best correction. Results: The most frequent causes of visual impairment involved the optic nerve (30.9%): optic atrophy, 13%; Leber's optic atrophy. 4.1%; optic nerve hypoplasia, 5.7%; and glaucoma, 8.1%. Other common causes included congenital malformations other than those categorized separately (primarily aniridia), 12.2%; cataracts/aphakia, 13.8%; albinism, 13.0%; and retinitis pigmentosa, 8.1%. Nystagmus, chorioretinitis, and other conditions accounted for the remaining 22% of diagnoses. Best-corrected visual acuity in the better eye ranged from 20/20 to no light perception (NLP), with 44.3% having acuity better than 20/200; 26.2% having 20/200 to less than 400; 13.1 % having measurable acuity of 20/400 or worse; 9% having light perception; and 7.4% having NLP. Conclusions: Optic nerve disorders are the most common cause of visual impairment at ASB. Relatively few students (16.4%) had no measurable visual acuity.