Primary hyperoxaluria is a congenital innate error of the metabolism of the amino acids, that is transmitted like an autosomal recessive character. Two types of hyperoxaluria exist: the primary type I, that corresponds to the peroxisomal enzymatic deficit of the alanine glyoxylate aminotransferase in the liver (AGT) and type II, due to the deficit of the glyoxylate reductase/hydroxypyruvate reductase deficiency (GRHPR). The primary type I (AGT) is the most frequenty. We report the case of a female infant of one month of age, that on her first day post birth, presented myoclonic convulsions and tonic spasms, both during wakefullness and sleep periods, that became more frequent and did not respond to the use of anticonvulsants. The ictal Electroencephalogram presented an intermittent activity of spikes and spike-waves of high voltage in the right hemisphere. Eight minutes after the intravenous administration of 150 mg of pyridoxine, it was observed a diminution of the epileptic activity, as well as the clinical manifestations. The determination of organic acids in urine revealed an increase in the concentration levels of oxalic acid (3064 mmol/mol of creatinine). The molecular genetic study of the AGXT gene, showed the existence of a R197Q mutation in exón 5 of the patient and her father. She received treatment with pyridoxine at a dose of 50 mg/day. When she reached the age of three months both a normal electroencephalogram and biochemistry were obtained. Although it is a rare cause of neonatal convulsions, hyperoxaluria, due to new mutations is an underdiagnosed disease by neonatologists and paediatricias.