Idiopathic acquired generalized anhidrosis is a very rare condition in which the pathogenesis is still unknown. Although varied findings have been reported, no consistent abnormal findings in sweat glands have been established by histological study or electronmicroscopic study. An 18-year-old Korean boy suffered from generalized anhidrosis after sunstroke. Physical and neurologic examination could not reveal any abnormal findings. There were no specific changes in the sweat glands, but amorphous vacuole-like structures were seen in the cytoplasm of secretary cells. We reviewed the previous reports about this rare condition and compared them with our patient.