Purpose Ketogenic dietary therapies (KDT) are high-fat and low-carbohydrate diets that may achieve seizure control and improve cognitive state. We describe our KDT experience in infants (children less than two years of age). Research methods & procedures We conducted a retrospective, descriptive and observational study of 42 infants treated with KDT between 2000-2018. Results The types of KDT started were: classic ketogenic diet ratio 3:1 (40), ratio 4:1 (1) and modified ketogenic diet with medium-chain triglycerides (1). Four patients switched to a modified Atkins diet. During follow-up, 79%, 57%, 38% and 17% of infants remained on KDT at 3, 6, 12 and 24 months, respectively. Seizure reduction ≥50% compared to baseline was achieved in 50%, 45%, 38% and 17% at 3, 6, 12 and 24 months, respectively. Seizure control was excellent (reduction >90%) in 33%, 31%, 26% and 12%, and seizure-free infants were 9, 9, 10 and 4, at different follow-up intervals, respectively. Sixty-three percent of infants with West syndrome were responders to KDT. Mean length of KDT was 390 days (16 days-4.9 years). Ineffectiveness was the reason for withdrawal in 50% of patients. Early adverse effects (during first month) occurred in 40% of infants. The most frequent early side effects were asymptomatic hypoglycemia and gastrointestinal disturbances. Late-onset side effects occurred in 55-14% of infants during therapy, and most frequent were hypercalciuria and dyslipidaemia. Conclusion KDT are useful and effective treatments in infancy. Side effects are frequent but mild and easy to manage.