We report a patient who presented with transient clumsiness of his right hand due to a small hemorrhage in the left globus pallidus. Ten days later, positron emission tomography performed at rest showed decreased oxygen metabolism and blood flow at the site of the anatomic lesion and in remote areas such as the ipsilateral frontotemporoparietal cortex and the contralateral cerebellar hemisphere. Cerebellar hypometabolism has been ascribed to functional disconnection of the contralateral hemisphere from the cerebral cortex and has been termed crossed cerebellar diaschisis. One month later, positron emission tomography performed during unilateral motor activation (finger opposition) showed increased blood flow in the sensorimotor and supplementary motor areas contralateral to the hand engaged in the motor task. An at-rest study at this time showed resolution of the crossed cerebellar diaschisis observed acutely, but cerebellar asymmetry was demonstrated during performance of the motor task with the normal as well as with the previously paretic hand. Our activation study demonstrated cerebellar asymmetry in the chronic phase during a motor task, even though resting cerebellar blood flow was symmetrical. This observation reveals the dynamic, functional nature of crossed cerebellar diaschisis and may partially explain the lack of any clinical counterpart in functional studies of the cerebellum performed with the patient at rest.