Argentinean newborn screening panel does not include the analysis of acylcarnitines and aminoacids by tandem mass spectrometry. There are currently no legislation regarding the use and conservation of RNBSBS. The aim of this work is to show how useful could be the storage of blood spots for retrospective diagnosis. A 4-month pregnant woman came to metabolic evaluation. Two previous children had died from severe liver failure of unknown cause. Autopsy was not performed; the only biological sample available was the RNBSBS from the last child. Acylcarnitines and aminoacids were analyzed on that sample. High levels of tyrosin(TYR), tyrosine/valine(TYR/VAL) ratio and succynil acetone(SUA) were found suggested Tyrosimenia type I. After birth samples were obtained from cord blood, 12, 24 and 48 hs of life. All the samples presented elevation of SUA, the 12hs sample also had a high TYR/VAL ratio with normal levels of TYR, and in the 24hs sample, TYR was also high. The newborn was put on NTBC treatment from day 4. After 1 and half year of follow-up the patient has a good evolution and better prognosis according the early onset of treatment. We demonstrate how important and helpful can be keeping RNBSBS for retrospective diagnosis of IEM.