Dopa-Responsive Dystonia (DRD) is a treatable neurological condition which can present with a variety of symptoms ranging from dystonia, spastic paraparesis, and proximal weakness to Parkinsonism. A family history of dystonia or Parkinson disease is common. At least 50% of patients have diurnal fluctuation with marked progression of their symptoms toward the end of the day and relief after sleep. The clinical features in patients with mutations in the GCH1 gene are characterized by pure dystonia with onset in the lower limbs and dramatic improvement with small doses of L-Dopa. Dystonia generally starts in the first decade, but later onset is also observed. In contrast to patients with Juvenile Parkinson’s disease, these patients do not usually develop levodopa-induced fluctuations or dyskinesia. There are at least three causative genes for DRD including genes that encode GTP cyclohydrolase 1 (GCH1), tyrosine hydroxylase (TH), and sepiapterin reductase (SPR). Females predominate among clinically affected individuals. Genetic testing should be guided by the analysis of cerebrospinal fluid levels of biopterin and neopterin, which are low in GTPCH1-deficient DRD. Prevalence of DRD in Japan and England is estimated at 1 in 2 million. No increased prevalence has been reported in any ethnic group.