A young woman with Westphal variant (juvenile) Huntington disease (HD) also developed catatonia. Catatonia is an underdiagnosed psychomotor syndrome often associated with neurological and psychiatric disorders, but it has rarely been documented in patients with HD. Catatonia usually responds to standard treatment with benzodiazepines and electroconvulsive therapy; however, this patient’s catatonic syndrome did not improve until we augmented the standard treatment with amantadine and levodopa. The underlying pathophysiology and a neurochemical hypothesis of HD and catatonia can explain their comorbidity and the refractoriness of catatonia to treatment. Both conditions are linked to dysregulation of neurotransmitters in the striatocortical and corticocortical pathways. This understanding may serve as a guide for the use of nonstandard treatments. Our evidence also suggests that electroconvulsive therapy can be useful and safe in the treatment of HD.