Background: Duplex ultrasound (DU) is used in the diagnosis of neurogenic thoracic outlet syndrome (NTOS) to measure compression of the subclavian artery (SCA) which is thought to strengthen the NTOS diagnosis. However, the value of DU in NTOS remains unclear. Methods: A retrospective review of a prospectively acquired database from the TOS center of the Catharina Hospital Eindhoven was performed of patients referred between January 2017 and December 2019. Only “proven NTOS” patients, defined as a successful response to thoracic outlet decompression (TOD) surgery based on patient-reported outcomes (NRS pain scale, CBSQ and DASH score) were included to exclude wrongfully diagnosed NTOS patient. The presence of vascular symptoms (defined as discoloration, edema or temperature changes of the hand or fingers), results of provocative maneuvers, and outcome of DU was used for analysis. To assess the link between vascular symptoms and compression on DU, a chi-squared test was performed. Further, we looked for a correlation between vascular symptoms, compression on DU and clinical outcome using a repeated measures analysis of variance (ANOVA). Results: Vascular symptoms were seen in 49 of 133 patients (36.8%). In total, 51 of 133 patients (38.3%) had at least 50% variation in SCA peak systolic velocity (PSV) during DU at the level of SCA stenosis. SCA occlusion was seen in 11 patients (8.3%) during provocative maneuvers. The presence of clinical “arterial symptoms” was not significantly correlated with vascular laboratory findings, neither for alterations in PSV during DU (P = 0.245) nor for positional SCA occlusion (P = 0.540). No statistically significant correlations between the degree of SCA stenosis and postoperative outcomes, as measured with the DASH, CBSQ, or NRS scale for pain were found (P = 0.787). Conclusions: The role of DU in the work-up of NTOS in patients with vascular complaints is questionable. Changes in flow velocities are seen in NTOS patients and do not correlate with “vascular symptoms” or clinical outcome.