Motor unit number estimation(MUNE) was performed in the thenar muscles of 22 hemiplegic patients without a peripheral nerve lesion using the statistical method. The studies were done bilaterally in the affected and unaffected sides. The distal latency and conduction velocity of median nerve in the affected side were not different from those in the unaffected side. But the amplitude and area of the compound muscle action potential in the affected side were smaller than those in the unaffected side. Motor unit numbers in the affected side decreased than those of the unaffected side, especially in the first 6 months after the onset of hemiplegia. And the motor unit numbers in the affected side decreased as the muscle strength decreased. Single motor unit potential(SMUP) area in the affected side increased after 1 year from the onset of hemiplegia. The estimation of the number of motor units in the thenar muscles of hemiplegic patients could be an indicator for predicting recovery of the muscle power in hemiplegia.