OBJECTIVE The purpose of this study was to investigate autonomic nervous system dysfunction by measuring pupil sizes in pediatric patients with allergic rhinitis. METHODS The study group consisted of 60 children (28 girls and 32 boys) who were age and gender matched with the control group, which also consisted of 60 children (26 girls and 34 boys). The diagnosis of allergic rhinitis was based on the history, physical examination and skin prick test performed by an allergologist. Pupil diameter measurements were performed using the pupillometer incorporated in the NİDEK OPD-Scan. RESULTS In the allergic rhinitis group, mean photopic and mesopic pupil diameters were 3.52 ± 0.07 and 5.98 ± 0.21, respectively, while in the control group, corresponding measurements were 4.03 ± 0.18 and 6.55 ± 0.16. There was a significant difference for photopic and mesopic pupil diameter between the groups (p < 0.001). CONCLUSIONS This study showed that the pupil size in response to a light stimulus in children with allergic rhinitis was smaller than that of the control group and may indicate parasympathetic hyperactivity and sympathetic hypoactivity.