A case of Hopkins syndrome is presented. The patient was a 4-year-old boy who developed weakness of the right leg 2-3 days after a mild asthmatic attack. Needle electromyography revealed fasciculation discharges in the right gastrocnemius muscle. A histological study of the biopsied right quadriceps femoris muscle revealed scattered atrophic fibers, indicating lesions in the anterior horn cells of the spinal cord. This is the first reported case of Hopkins syndrome including muscle pathology.