Benign monomelic amyotrophy(BMA) is an uncommon cause of progressive mildly disabling atrophy and weakness of a limb. It predominantly affects the distal upper limb of young men. I present two men with BMA of the lower extremities. Although the disorder seemed clinically confined to a arm or leg, I confirmed by electromyography evidence of denervation in the other extremities. I reviewed the literatures and discuss the differential diagnosis. BMA is a diagnosis. BMA is a diagnosis of exclusion that requires consideration in men with unilateral arm or leg atrophy and weakness.
