The modified Atkins diet is a dietary therapy for intractable epilepsy that mimics the ketogenic diet, yet does not restrict protein, calories, and fluids. The ideal starting carbohydrate limit is unknown. Twenty children with intractable epilepsy were randomized to either 10 or 20 g of carbohydrates per day for the initial 3 months of the modified Atkins diet, and then crossed over to the opposite amount. A significantly higher likelihood of >50% seizure reduction was noted for children started on 10 g of carbohydrate per day at 3 months: 60% versus 10% (P=0.03). Most parents reported no change in seizure frequency or ketosis between groups, but improved tolerability with 20 g per day. A starting carbohydrate limit of 10 g per day for children starting the modified Atkins diet may be ideal, with a planned increase to a more tolerable 20 g per day after 3 months.