Obstructive sleep apnea (OSA) is prevalent in the middle-aged and elderly population. OSA causes sleep fragmentation with intermittent oxygen desaturation and is the most common cause of excessive sleepiness, which often improves after treatment. Narcolepsy is a neurological disorder and is another common cause of excessive sleepiness. However, coexistent narcolepsy in OSA patients is uncommon. Unlike OSA, narcolepsy is rarely discovered among elderly people. Therefore, we report an elderly OSA patient co-morbid with narcolepsy, a very rare condition in clinical practice.