This is a prospective cohort study of 237 children (130 males, 107 females) placed on the ketogenic diet for control of intractable epilepsy (mean age at starting diet 3 years 8 months; age range 2 months to 9 years 10 months); average length of follow-up was 308 days. There were 133 children on the diet at 1 year and 76 at 2 years. Height and weight measurements were converted into age- and sex-appropriate z scores. There was a rapid drop in weight z scores in the first 3 months. After this initial period, the weight z score remained constant in children who started the diet below the median weight for their age and sex, although z scores continued to decrease in children starting above the median. There was a small decrease in height z scores in the first 6 months (<0.5); however, there were larger changes by 2 years. There was no difference based on sex for either height or weight. The ketogenic diet generally provides sufficient nutrition to maintain growth within normal parameters over a defined period. Very young children grow poorly on the diet and should be followed-up carefully over long periods of use.