Purpose. To determine the natural history of patients presenting with acute proximal biceps rupture (APBR) and concomitant rotator cuff disease. Methods. Prospective cohort study of patients with an APBR confirmed via magnetic resonance imaging (MRI) presenting to clinic within 8 weeks of injury. Visual Analog Scale (VAS) pain score, Simple Shoulder Test (SST) score, and the American Shoulder and Elbow Surgeons (ASES) score were the main outcome measures assessed at a minimum of two-years. Results. Twenty-seven patients were included in the final analysis: seven females (26%) and 20 males (74%) (mean age: 61 years, range 42-78 years). Rotator cuff tears were found in 25 patients (93%). At two-year follow-up (SD 0.28), nine patients (33%) without improvement or dis-satisfaction with conservative management opted to undergo shoulder surgery (all with rotator cuff tears), at a mean 4.5 months (range 1.2-24 months) after injury. Worker's Compensation and a history of diabetes were significantly associated with having surgery. At the two-year follow-up, the median patient reported outcomes (PROs) were as follows: VAS pain- 0.0 (IQR 0.0-3.0); Disability subscale- 48.3 (IQR 34.2-50.0); ASES total- 89.2 (IQR 70.0-98.3); and SST- 11.0 (IQR 9.0-12.0). There was no statistically significant difference in PROs between patients who went on to have surgery and those who did not. Conclusions. Satisfactory PROs and low levels of pain were reported at the two-year follow-up in patients with an APBR, with no difference between those patients who underwent surgical intervention and those who did not. [ABSTRACT FROM AUTHOR]