Glucose transport protein deficiency due to mutation in the GLUT1 gene is characterized by infantile onset and chronic seizure disorder, microcephaly, global developmental delays, and hypoglycorrhachia. We describe a 10‐year‐old normocephalic male with prominent ataxia, dystonia, choreoathetosis, and GLUT1 deficiency whose motor abnormalities improved with a ketogenic diet. We illustrate the motor abnormalities, at baseline and after ketogenic diet, that characterize this unusual case. This case broadens the phenotype of GLUT1 deficiency and illustrates the importance of cerebrospinal fluid (CSF) evaluation in detecting potentially treatable conditions in children with undiagnosed movement disorders. © 2005 Movement Disorder Society