Purpose:  In 2002, we reported our preliminary experience using the ketogenic diet (KD) for predominantly intractable infantile spasms (IS) in 23 infants. Since that time, we have increased our use of the KD for this condition including those with new‐onset IS.

Methods:  Infants were referred and prospectively started on the traditional KD from 1996 to 2009 at our institution. Included subjects had documented clinical IS, hypsarrhythmia on electroencephalography (EEG), and parental consent to start the KD. Efficacy was assessed through phone communication, clinic visits, and EEG every 3 months.

Results:  One hundred four infants, mean age 1.2 years, were started on the KD for IS, of which 74 (71%) had a symptomatic etiology. Previous therapy for this patients included a mean of 3.6 anticonvulsants; 71% including corticosteroids or vigabatrin. Using an intent‐to‐treat analysis, >50% spasm improvement occurred in 64% at 6 months and 77% after 1–2 years. Thirty‐eight (37%) became spasm‐free for at least a 6‐month period within a median 2.4 months of starting the KD. In addition, 62% reported improvement in development, 35% had EEG improvement, and 29% were able to reduce concurrent anticonvulsants. Adverse effects were noted in 33%, of which 6% had diminished linear growth. Older age at onset of IS and fewer prior anticonvulsants were more likely to be associated with >90% spasm improvement at 6 months.

Discussion:  The KD is an efficacious therapy for IS in approximately two‐thirds of patients treated, and it should be considered strongly after failure of corticosteroids and vigabatrin.