To report a case of benign monomelic amyotrophy of lower limb (BMALL), and to explore the etiology, pathogenesis, clinical manifestations, auxiliary examination, diagnosis and prognosis of the disease in accordance with the literature. Methods: The clinical data of this patient were analyzed retrospectively. The related domestic and foreign literatures were retrieved and analyzed. Results: Four years ago, the patient found muscle atrophy of his right lower limb with no obvious incentive, gastrocnemius involved mainly. Muscle atrophy gradually progressed upward. Compared with muscle atrophy, muscle weakness was relatively mild. There were no paresthesia, pyramidal signs and medullary damage. Physical examination showed normal right leg muscle tension, muscle strength 5— grade, tendon reflexes (-), no fasciculation fibrillation, pathological sign (-). Muscle MRI showed right lower extremity gastrocnemius, soleus muscle, anterior tibialis, quadriceps and gluteus maximus have varying degrees of atrophy. EMG showed right lower extremity neurogenic damage. Right quadriceps muscle biopsy showed neurogenic muscular atrophy. In previously reported 95 cases of BMALL patients, more patients were male, all patients had no symptoms of muscle weakness, and a small part had mild sensory abnormalities. Electromyograms of all patients showed neurogenic damage, and muscle biopsy all showed neurogenic muscle atrophy. Most patients have a good prognosis after several years of follow-up. Conclusion: BMALL is a relatively benign neuromuscular disease. The clinical manifestations are unilateral lower limb atrophy, muscular atrophy and myasthenia gravis disproportionately. The onset of symptoms is insidious and the progression is slow without affecting daily life. The etiology and pathogenesis are not clear currently. The diagnosis depends mainly on medical history, physical examination, muscle magnetic resonance, electromyography and muscle biopsy. There is no specific treatment. Generally, BMALL has benign progress, but there are a few cases of poor prognosis.