This article describes a case of pyruvate dehydrogenase deficiency in a 3-year-old boy who presented generalized hypotonia, severe psychomotor development delay, and generalized and partial seizures and was refractory to antiepileptic drugs. After the diagnosis, the patient was put on a ketogenic diet. Six months later, seizure frequency was reduced and psychomotor development had improved. At the same time he presented some side effects, such as 2 episodes of significant increases in cholesterol and triglycerides associated with viral respiratory infections. The latter decreased with a supplementation of ω-3 fatty acids and an increase in caloric intake.