Familial amyotrophic lateral sclerosis. A case of familial amyotrophic lateral sclerosis (ALS) in a family with hereditary motor and sensory neuropathy type 1 (HMSN-I) is reported. A 32-year-old man, the youngest son of a father with HMSN-I, developed progressive weakness of the bilateral upper and lower limbs, while motor nerve conduction velocities (MCV) of the median nerves showed no delay. His older brother had HMSN-I and a family history of this disease was confirmed. A sural nerve biopsy obtained from the affected brother demonstrated reduction and loss of large myelinated fibers as well as an increase in the number of small axons and axons with an abnormal morphology. Ultrastructural studies revealed demyelinating changes, axon loss, and remyelination. No neurofibrillary tangles or Hirano bodies were noted. Onset of symptoms was early in our case, but this seems to be common in this family. A close relationship between HMSN-I and ALS is suggested.