Epileptic seizures can occur in many inborn errors of metabolism (IEMs), usually as part of a larger clinical spectrum. This chapter considers IEMs, most of which are amenable to specific metabolic treatment. Epilepsy is frequent in Glucose transporter type 1 (GLUT-1) deficiency. Hyperinsulinism/hyperammonemia syndrome (HI/HA) is a rare disorder resulting from missense mutations in glutamate dehydrogenase. Non-ketotic hyperglycinemia (NKH) results from mutations in the subunits of the glycine cleavage enzyme that degrades the neurotransmitter glycine. The congenital disorder of glycosylation (CDG) syndrome covers a group of autosomal recessive diseases, resulting from mutations in the enzymes responsible for protein glycosylation. Epileptic patients, when an IEM is suspected, should have a complete clinical examination, EEG, brain magnetic resonance imaging (MRI) with proton magnetic resonance spectroscopy, ophthalmologic examination, and abdominal ultrasonography. Practical efforts should be made to identify the IEM that can benefit from tailored metabolic therapies.