Diagnosing thoracic outlet syndrome relies on combining what the patient reports and what the clinician finds during a focused examination. The clinical evaluation is essential because it helps characterize the symptom pattern (neurogenic vs vascular), localize the area of compression, and identify provocative maneuvers that reproduce symptoms. These findings guide further testing and management, but they aren’t definitive on their own. Imaging and objective studies add crucial confirmation and detail. Imaging can reveal anatomical causes such as cervical ribs, scalene muscle hypertrophy, or postural issues that contribute to compression, while vascular studies (like duplex ultrasound or MR/CT angiography) assess blood flow and help distinguish vascular from neurogenic forms. Nerve conduction studies and electromyography can support a neurogenic diagnosis and rule out other conditions. Because no single test proves thoracic outlet syndrome, the diagnosis is best made with clinical evaluation integrated with imaging and studies.