We described the clinical status and computerized tomographic findings of two patients with tetrahydrobiopterin (BH4) deficiency due to impaired BH4 regeneration. In addition to an unfavorable course, cranial computerized tomography scans demonstrated severe cortical and subcortical atrophy and bilateral corticomedullary and basal ganglia calcifications in these two cases. The occurrence of calcification in the same distribution following the use of methotrexate, a folic acid antagonist, supported the hypothesis that there is a link between the metabolism of pterins and folate.