Diagnosis of Non-Ketotic Hyperglycinemia by MSMS newborn screening might benefit patients with post-neonatal presentation. We screened 733,527 babies over eight years, and nine babies were subsequently diagnosed with NKHG. Two had newborn glycine levels above our cut-off and presented within 72 h. The remaining patients could not have been diagnosed by newborn screening without an unacceptably high recall rate. We conclude that babies with NKHG are not usually identifiable by current newborn screening strategies.