Nocturnal enuresis (NE) is a syndrome associated with abnormal nocturnal urine production, urination mechanism, and sleep arousal. NE is strongly associated with attention-deficit/hyperactivity disorder (ADHD), and it has been reported that NE occurs in approximately 30% of children with ADHD. There have been several reports on the efficacy of atomoxetine as treatment for NE with ADHD, while the efficacy of guanfacine is still limited. We report our experience of treating an 10-year-old girl with NE with ADHD with a single dose of guanfacine. The patient first visited our hospital because of difficulty concentrating, restlessness at home and school, and nocturnal incontinence. She was diagnosed with NE with ADHD based on a review of her personal history from her mother. Her NE symptoms improved with guanfacine monotherapy (1 mg/day. The patient weighed 28 kg).