Objective Neurogenic thoracic outlet syndrome (NTOS) is caused by dynamic compression of the brachial plexus at the level of the supraclavicular scalene triangle or the subcoracoid (pectoralis minor) space, or both. The purpose of this study was to characterize relationships between 14 clinical diagnostic criteria (CDC) and seven pretreatment patient-reported outcomes measures (PROMs) in a prospective cohort of patients with NTOS. Methods There were 183 new patient referrals between July 1 and December 31, 2015, with 150 (82%) meeting an established set of predefined CDC for NTOS. PROMs were evaluated across five domains: pain severity, functional disability, depression, quality of life, and pain catastrophizing. Linear regression and Pearson correlation statistics were used to analyze associations between CDC and PROMs. Results Mean ± standard error patient age was 37.1 ± 1.1 years (range, 12-66 years), and 107 (71%) were women. Five (3%) had a cervical rib, and 15 (10%) had recurrent NTOS. The most frequently positive CDC were neck or upper extremity pain (99%), upper extremity or hand paresthesia (94%), symptom exacerbation by arm elevation (97%), localized supraclavicular or subcoracoid tenderness to palpation (96%), and a positive 3-minute elevated arm stress test (94%; mean duration, 102.0 ± 5.1 seconds). The number of positive CDC (mean, 9.6 ± 0.1) correlated with the degree of tenderness to palpation and the duration of elevated arm stress test, as well as with PROMs for pain severity, functional disability, depression, physical quality of life, and pain catastrophizing (all P <.0001). PROMs across multiple domains were also strongly correlated with each other. Patients with clinically significant pain catastrophizing exhibited a greater level of functional disability than noncatastrophizing patients (P <.0001). Conclusions This study illustrates the relative strengths of 14 CDC and seven PROMs to evaluate patients with NTOS, helping validate the selected CDC and highlighting the potential role of pain catastrophizing in functional disability. This cohort will provide valuable information on the utility of different CDC and PROMs to predict treatment outcomes.