Neurogenic thoracic outlet syndrome (NTOS) is a chronic painful and disabling condition. Patients complain about upper-limb paresthesia or weakness. Weakness has been considered one of the diagnostic criteria of NTOS, but objective comparisons to healthy controls are lacking. We compared the grip and the key pinch strengths between NTOS patients and healthy controls. Grip strength was evaluated with a hydraulic hand dynamometer and the key pinch with a pinch gauge. All the patients with NTOS completed a QuickDASH. We included prospectively 85 patients with NTOS, 73% female and 27% male. The mean age was 40.4 ± 9.6. They were compared to 85 healthy subjects, 77.6% female and 22.4% male. Concerning the grip, symptomatic hands of NTOS patients had significantly 30% less strength compared to control hands (p ≤ 0.001), and 19% less strength compared to asymptomatic hands (p = 0.03). Concerning the key pinch, symptomatic hands of patients with NTOS had significantly 19.5% less strength compared to control hands (p ≤ 0.001). Grip and key pinch strengths had a significant correlation with the QuickDASH (r = −0.515 and r = −0.403, respectively; p ≤ 0.001). Patients with NTOS presented an objective hand strength deficit compared to healthy controls. This deficit was significantly correlated to the upper-limb disability. These findings confirm the interest of hand strength evaluation in the diagnostic process of patients with NTOS.