Unilateral hyperhidrosis of neurological origin has been associated with head trauma, cerebral palsy, spinal cord injury, peripheral neuropathy, lesions of the hypothalamus, and cerebral or brainstem strokes. In this report, we describe a 61-year-old man with isolated sweating on the left side of his entire body. A right-sided brainstem meningioma producing mass effect is suspected as the underlying etiology.