Although amyotrophic lateral sclerosis and progressive spinal muscular atrophy have been recognized to occur in association with human immunodeficiency virus infection, to our knowledge, brachial amyotrophic diplegia, a form of segmental motor neuron disease, has not been previously reported. Brachial amyotrophic dip legia results in severe lower motor neuron weakness and atrophy of the upper ext remities in the absence of bulbar or lower extremity involvement, pyramidal feat ures, bowel and bladder incontinence, and sensory loss. We describe a human immu nodeficiency virus-seropositive man without severe immunosuppression or prior A IDS-defining illnesses who had brachial amyotrophic diplegia. This disorder may represent one end of a spectrum of motor neuron diseases occurring with this re trovirus infection. Although amyotrophic lateral sclerosis and progressive spinal muscular atrophy have been recognized to occur in association with human immunodeficiency virus infection, to our knowledge, brachial amyotrophic diplegia, a form of segmental motor neuron disease, has not been previously reported. Brachial amyotrophic dip legia results in severe lower motor neuron weakness and atrophy of the upper ext remities in the absence of bulbar or lower extremity involvement, pyramidal feat ures, bowel and bladder incontinence, and sensory loss. We describe a human immu nodeficiency virus-seropositive man without severe immunosuppression or prior A IDS-defining illnesses who had brachial amyotrophic diplegia. This disorder may represent one end of a spectrum of motor neuron diseases occurring with this re trovirus infection.