Carnitine palmitoyl transferase (CPT) 1 A deficiency is a rare disorder of hepatic long-chain fatty acid oxidation. CPT1 deficiency is included in newborn screening programs in a number of countries to allow presymptomatic detection and early treatment of affected patients.We present a case of presymptomatic CPT1A deficiency detected through newborn screening in Denmark with diagnostic levels of carnitine and acylcarnitines in the initial dried blood spot. Levels of plasma-free carnitine and acylcarnitines in follow-up samples were normal, but reverted to diagnostic levels when the patient developed clinical symptoms at the age of 8 months. At that time, a diagnosis of CPT1A deficiency was confirmed by sequence analysis of the CPT1A gene revealing homozygosity for a novel c.167C>T variation in exon 3. Enzyme activity measurements showed a relatively mild enzyme defect with a decreased residual enzyme activity of 17-25%. We conclude that CPT1A gene testing and/or enzyme assay is mandatory to confirm an abnormal newborn screen suggesting CPT1A deficiency to avoid delayed diagnoses.