Strabismus is associated with amblyopia and a lower quality of life. Attention-deficit hyperactivity disorder (ADHD) is common among children and adolescents, and influences their academic, vocational, and social life. Previous studies have suggested an association between strabismus and ADHD. Using data from the Taiwan National Health Insurance Research Database between 2000 and 2010, we performed a large-scale cohort study comparing the incidence, risk factors, and severity of ADHD in children with and without strabismus. A total of 2049 patients <18 years old with newly diagnosed strabismus (esotropia: 404; exotropia: 1645) were identified, and 8196 age- and sex-matched controls without strabismus were also included. After an average of 6.5 ± 2.9 years of follow-up, the incidence of ADHD per 1000 person-years was 5.39 in the strabismus group (esotropia: 9.93; exotropia: 4.11) and 3.23 in the control group. The cumulative incidence of ADHD was significantly greater in the esotropia (hazard ratio [HR]: 2.04; 95% confidence interval [CI]:1.36-3.06; = 0.0007) and exotropia groups (HR: 1.44; 95% CI: 1.03-2.03; = 0.038) than in the controls. Patients with strabismus had more comorbidities than those without ( < 0.05). In summary, this large-scale study found a higher cumulative incidence of ADHD in patients with strabismus, especially in those with esotropia.