The persistent vegetative state (PVS) and the minimally conscious state (MCS) are conditions of altered consciousness after severe brain damage due to a variety of pathologies. However, the specific pathophysiological mechanisms and a therapeutic strategy for intervention have not as yet been established. We review previous reports of levodopa treatment for patients in PVS, MCS, or other mental disorders, and have focused on five representative cases: four of PVS and one of MCS after severe brain injury. In summary, our review suggests the effectiveness of levodopa treatment is probably dependent upon the following criteria: (1) Diagnosis of PVS or MCS as distinct from other related conditions, (2) Concomitant symptoms of parkinsonism, and (3) Concomitant neuroradiological findings of high intensity lesions in the dopaminergic pathway on T2 weighted MRI. The apparent success of levodopa in the five cases described may reflect a specific subgroup of PVS and MCS patients, where the administration of levodopa is effective. However, we should not regard PVS or MCS as a single entity, since levodopa is unlikely to be effective in all cases. Therapeutic strategies should aim to identify the key pathophysiological mechanism for each patient and target interventions accordingly.