BackgroundRelatively weak correlations between patient symptoms and rotator cuff tendon (RCT) tearing have been reported; however, the relationship between symptoms and tendinosis has been less well‐studied.Purpose/HypothesisTo use quantitative MRI to assess the bilateral RCTs in shoulders of both patients with unilateral symptomatic tendinopathy and control subjects. We hypothesized that quantitative MRI measures would differ between symptomatic patients and controls.Study TypeProspective imaging study.Population/SubjectsIn all, 48 shoulders from 24 subjects (mean age, 32.8 years), including 14 patients with unilateral symptomatic tendinopathy and 10 asymptomatic controls.Field Strength/Sequence3T/3D ultrashort echo time Cones sequence with magnetization transfer preparation (UTE‐Cones‐MT) and Carr–Purcell–Meiboom–Gill.AssessmentMacromolecular fraction (MMF) and T2 relaxation were measured in four regions of the superior RCT, including all‐segments, and lateral‐third, bursal‐sided, and articular‐sided segments. The Western Ontario Rotator Cuff (WORC) index and visual analog scale were assessed.Statistical TestsThree shoulder groups were evaluated, including symptomatic shoulders, contralateral asymptomatic shoulders in patients, and asymptomatic controls. MMF and T2 values were compared between groups using a bootstrap‐based comparison of means.ResultsSignificant differences were found in both MMF and T2 values between symptomatic and control RCTs when analyzing all‐segments (P = 0.027 and P = 0.006, respectively) and articular‐sided segments (both P = 0.001). Significant differences between asymptomatic RCTs in patients and control RCTs were also found, including MMF in all four anatomic regions analyzed (P = 0.024–0.044), as well as T2 in all‐segments (P = 0.003), bursal‐sided segments (P = 0.021), and articular‐sided segments (P = 0.002). No significant differences in MMF (P = 0.420–0.950) or T2 (P = 0.380–0.910) were seen between ipsilateral symptomatic and contralateral asymptomatic RCTs in patients.Data ConclusionSymptomatic RCTs showed significantly lower MMF values and higher T2 values compared with control RCTs. In patients with unilateral symptomatic tendinopathy, the contralateral shoulder can demonstrate asymptomatic tendinopathy, which can be quantified using MMF or T2.Evidence Level2Technical EfficacyStage 2. J. Magn. Reson. Imaging 2020;52:864–872.