To evaluate intelligence quotient (IQ) in patients with congenital strabismus.All patients with congenital strabismus scheduled for surgery were enrolled consecutively over a one year period in a cross-sectional study and were evaluated for verbal, performance and total IQ scores, and compared to the mean normal IQ of 100±15.During the study period, 109 patients with mean age of 18.4±10.5 (range, 4-63) years were included. Educational status in most patients (80%) was less than high-school. Most patients (80%) lived in urban areas and 46 patients (42.2%) had some degrees of unilateral or bilateral amblyopia. Mean verbal IQ was 87.2±19.6 (range, 45-127), performance IQ was 81±15.5 (range, 44-111) and total IQ was 83.5±18.3 (range, 40-120). Total IQ was significantly lower in comparison to the normal population (P0.05 for all comparisons).Patients with congenital strabismus in this study had lower mean IQ scores than the normal population which may be due to genetic background or acquired causes secondary to strabismus.