One of the most important therapeutic goal in hyperhidrosis treatment is to seek for the underlying cause and to tailor the treatment accordingly. A detailed history and prompt physical examination are needed to clarify the etiological factor. In this study, we report a 34-year-old woman with a diagnosis of thoracic outlet syndrome presenting with complaints of pain, numbness, and fatigue in her left arm and ipsilateral palmar hyperhidrosis. Thus, we want to highlight a specific potential cause of secondary hyperhidrosis, which can otherwise be easily overlooked, and furthermore, which has a completely different treatment strategy.