Dopa-responsive dystonia in children, including guanosine triphosphate cyclohydrolase I deficiency, is an important subcategory of treatable dystonia characterized by a dramatic, sustained response to levodopa. Early diagnosis is difficult, however, because of the heterogeneity of the clinical phenotype. We report on two Korean children affected with dopa-responsive dystonia caused by a novel missense mutation of the guanosine triphosphate cyclohydrolase I gene. One child exhibits a novel sporadic mutation, and the other child demonstrates autosomal-dominant inheritance.