We studied the histopathology of spastic muscles in patients with spastic cerebral palsy using specimens obtained from the gastrocnemius muscles during orthopedic operations. Though there was no disease-specific abnormality, we found changes in fiber type distribution, i.e., type-1 fiber predominance and type-2B fiber deficiency. These changes were not found in the patient with brain infarction at age 1 year 5 months. Variation in fiber size, especially in type-1 fibers, was also detected in older patients and at the more severely affected sides. We speculated that the influence on the spinal motor unit from upper motor cortex might be applicable to the muscle histological findings and the time of the onset of the brain damage might be important.