Somnambulism or sleepwalking is a disorder classified as non-rapid eye movement sleep parasomnia and is common in adolescents. Sleep fragmentation occurs frequently in somnambulism, and waking up and wandering are the main symptoms of the disorder. Our patient was a 14-year-old male with a 3-year history of sleepwalking at night when he visited our sleep clinic. A polysomnography was performed for the evaluation of parasomnia. Our patient was diagnosed as having parasomnia overlap syndrome with moderate obstructive sleep apnea (OSA). Continuous positive airway pressure (CPAP) therapy was prescribed for the OSA. After 12 weeks of CPAP, not only did the patient’s OSA symptoms resolve but somnambulism disappeared. Previous reports of overlap syndrome with OSA and somnambulism also supported the use of CPAP treatment for patients with both OSA and somnambulism.