Non-ketotic hyperglycinaemia is an autosomal recessive disorder of glycine metabolism caused by a defect in the glycine cleavage system. Affected neonates present with lethargy, feeding difficulty, hypotonia, apnoea, poorly controlled convulsions and coma. Four cases are reported, three of whom died in the neonatal period. The fourth case was treated with dextromethorphan and sodium benzoate. He survived with neurodevelopmental delay but is now almost seizure-free.