A case of a child presenting with congenital abnormalities at birth is reported. The early development remained severely retarded and acquired skills minimally. The head circumference centile decreased. Magnetic resonance imaging showed progressive neuronal atrophy and secondary delay in myelination. Dihydropyrimidine concentrations in body fluids were quantitated by NMR spectroscopy. Enzymatic assay in the liver biopsy revealed total deficiency of dihydropyrimidinase (DHP) (5,6-dihydropyrimidine amidohydrolase; EC 3.5.2.2). As such, the patient is the first with enzymatically proven DHP deficiency. Thus far dihydropyrimidinuria has been reported in three other patients with a variety of neurological abnormalities. A relation of the enzyme deficiency with the neurodegenerative clinical course in our patient is suggested.