Background: The literature has shown good results with partial repairs of large and massive tears of rotator cuff but the role of factors that affect reparability is less clear. The purpose of this study was twofold, 1) to examine clinical outcomes following complete or partial repair of large or massive full-thickness rotator cuff tear, and 2) to explore the value of clinical and surgical factors in predicting reparability. Methods: This was a secondary data analysis of consecutive patients with large or massive rotator cuff tear who required surgical treatment (arthroscopic complete or partial repair) and were followed up for two years. Disability measures included the American Shoulder and Elbow Surgeons (ASES), the relative Constant-Murley score (CMS) and the shortened version of the Western Ontario Rotator Cuff Index (ShortWORC). The relationship between predictors and reparability was examined through logistic regressions and chi-square statistics as appropriate. Within group change over time and between group differences in disability outcomes, range of motion and strength were examined by student's T-tests and non-parametric statistics. Results: One hundred and twenty two patients (41 women, 81 men, mean age 64, SD = 9) were included in the analysis. There were 86 large (39 fully reparable, 47 partially reparable) and 36 (10 fully reparable, 26 partially reparable) massive tears. Reparability was not associated with age, sex, or pre-operative active flexion or abduction (p >0.05) but the fully reparable tear group showed a better pre-operative ASES score (p = 0.01) and better active external rotation in neutral (p = 0.01). Reparability was associated with tear shape (p < 0.0001), size (p = 0.002), and tendon quality (p < 0.0001). Conclusions: Reparability of large or massive tears is affected by a number of clinical and surgical factors. Patients whose tears could not be fully repaired showed a statistically significant improvement in range of motion, strength and disability at 2 years, although they had slightly inferior results compared to those with complete repairs.