L-2-hydroxyglutaric aciduria (L2HGA) is a chronic slowly progressive neurodegenerative disease characterized mainly by psychomotor developmental delay and cerebellar dysfunction. We report the clinical, biochemical, and neuroimaging features of 29 patients from 22 families. The mean age at the time of diagnosis was 13.4 years (2.5-32 years). The mean follow-up period of patients was four years (1.5-16 years). The main clinical findings were mental retardation and cerebellar involvement with ataxic gait and intentional tremor. Additional findings were mental retardation, macrocephaly and seizures. Diagnosis was confirmed by increased urinary excretion of L-2-hydroxyglutaric acid in all patients and highly specific magnetic resonance imaging (MRI) pattern showing subcortical leukoencephalopathy with bilateral high signal intensity in dentate nuclei and putamens. During the follow-up period, all patients had a static encephalopathy course. The underlying metabolic defect and the possible role of L-2-hydroxyglutaric acid are studied in a subgroup of these families and under evaluation for publication.