Functional enuresis is defined as repeated voiding of urine into bed or clothes in children after 5 years of age following the exclusion of major somatic diseases. Autonomic nervous system dysregulation has been proposed as a pathophysiologic mechanism in the etiopathogenesis. The objective of this study was to evaluate autonomic nervous system functions with pupil diameter measurement in enuretic children. The study group consisted of 17 children with functional enuresis (ten boys, seven girls), and the control group consisted of 34 healthy children (20 boys, 14 girls). Pupil diameter measurements were performed under photopic and mesopic lighting conditions by using a pupillometer. Mean photopic pupil diameter was found to be larger in the enuretic children than in the healthy controls (4.47 +/- 0.52 mm vs. 4.03 +/- 0.75 mm; P = 0.03). Autonomic nervous system imbalance of the ocular system is considered to be part of the autonomic nervous system dysregulation in functional enuretic children.