The effects of a low-carbohydrate, ketogenic diet (LCKD) on sleepiness and other narcolepsy symptoms were studied. Nine patients with narcolepsy were asked to adhere to the Atkins' diet plan, and their symptoms were assessed using the Narcolepsy Symptom Status Questionnaire (NSSQ). The NSSQ-Total score decreased by 18% from 161.9 to 133.5 (p = 0.0019) over 8 weeks. Patients with narcolepsy experienced modest improvements in daytime sleepiness on an LCKD.