A neonate at risk for hepatic carnitine palmitoyltransferase I (L-CPT I) deficiency was investigated from birth. The free carnitine and acylcarnitine profile in dried whole blood filter paper samples collected at ages 1 and 4 days showed a markedly elevated concentration of free carnitine (141 and 142 micromol/L, respectively), normal concentrations of acetyl- and propionylcarnitine, with the near absence of all other species. The diagnosis was confirmed by in vitro fatty acid oxidation screening assays and enzyme assay in cultured skin fibroblasts. Retrospective study of the newborn whole blood sample of the index case showed a similar profile (free carnitine 181 micromol/L). The newborn population distribution of free carnitine (n = 143,981) showed that only three samples had free carnitine > 140 micromol/L (>99.9th centile), two were from L-CPT I-deficient neonates and one from a baby with sepsis. While there are other conditions that can cause elevated concentrations of free carnitine, an isolated elevation of free carnitine only in an apparently healthy term neonate warrants further investigation to exclude L-CPT I deficiency.