Ten adults were treated with ketogenic diet monotherapy for epilepsy. Four patients were naïve to antiseizure drugs (ASDs), and six previously tried and stopped ASDs. Of four treatment-naïve participants, two (50%) were free from disabling seizures on Modified Atkins Diet (MAD) monotherapy for > 1 year. Two (50%) stopped. Four of six patients (67%) who had previously tried ASDs became seizure-free on diet monotherapy, and two experienced > 50% seizure reduction. Side effects included amenorrhea, weight loss, osteoporosis, and hyperlipidemia. Diet monotherapy may be feasible, well-tolerated, and effective for adults with epilepsy who refuse pharmacotherapy and those for whom lifelong diet therapy is recommended.