Clinical picture of neuronal ceroid lipofuscinosis with late infantile onset (LINCL) is characterized by myoclonic seizures and psychomotor regression. We present a case of classic LINCL and reduced cerebrospinal fluid (CSF) pterins in a girl of normal psychomotor development and born to non-consanguineous parents. She first presented with febrile seizures at the age of four. At that time, brain computed tomography finding was normal, but electroencephalogram showed hypsarrhythmia. At the age of five, tremor, generalized ataxia, and motor and mental regression appeared. Brain magnetic resonance imaging showed cerebellar atrophy. Electron microscopy examination showed storage of intracytoplasmic curvilinear inclusions in neurons, fibroblasts, and secretory cells of the skin and rectal mucosa. Tripeptidyl peptidase I (TPP-I) activity in leukocytes was very low (5.4 nmol/h/mg protein; range in homozygote cases of LINCL, 0.4-26.0). Molecular genetic studies showed a homozygous mutation, R208X, in exon 6 of CLN2 gene. CSF analysis revealed very low neopterin (7.3 nmol/L; normal range, 9-30) and biopterin (4.1 nmol/L; normal range, 10-30), reduced homovanillic acid (266 nmol/L; normal range, 211-871), and low homovanillic acid/5-hydroxyindoleacetic acid ratio (1.21; normal ratio, 1.5-3.5). Treatment with L-Dopa/Carbidopa (4 mg/kg) and antiepileptics was introduced, but without significant effect. It seems that low CSF pterins and impaired dopamine turnover are secondary manifestations of classical LINCL caused by homozygous inheritance of the R208X mutation in CLN2 gene.