AIM: To investigate the clinical characteristics of sibling patients with comitant strabismus. METHODS: Sibling patients who were diagnosed with comitant strabismus from January 2005 to December 2014 were retrospectively reviewed. Factors including age, sex, types of strabismus, refractive errors, angle of deviation, and coexistence of other strabismus were analyzed. RESULTS: A total of 62 patients (31 pairs of siblings) were included. Of these, 26 pairs had intermittent exotropia, 3 had accommodative esotropia, and 2 had infantile esotropia. There were no pairs with different subtypes of strabismus. The age at first visit was 3.7±2.6y and the mean follow-up period was 30.5±24.1mo. In siblings with intermittent exotropia, there was no difference in age of onset, age at operation, or refractive errors between the first and second-born children. The 20 (77%) pairs of siblings with exotropia showed more than 80% concordance of maximum angle of deviation during follow-up. In the 9 pairs in which both siblings had an operation, the final angle of deviation after the operation was 8.2±8.1 prism diopters (PD) in first-born children and 8.6±6.5 PD in second-born children. CONCLUSION: The subtypes of strabismus are the same in all pairs of siblings and clinical characteristics of strabismus are similar between the first and second-born children. This similarity could be an indicator for the diagnosis of second-born children. Further prospective study including a larger number of sibling patients is needed.