Background: Very little comparative information is available regarding the demographic and morphological characteristics of asymptomatic and symptomatic rotator cuff tears. This information is important to provide insight into the natural history of rotator cuff disease and to identify which factors may be important in the development of pain. The purpose of the present study was to compare the morphological characteristics and prevalences of asymptomatic and symptomatic rotator cuff disease in patients who presented with unilateral shoulder pain. Methods: Five hundred and eighty-eight consecutive patients in whom a standardized ultrasonographic study had been performed by an experienced radiologist for the assessment of unilateral shoulder pain were evaluated with regard to the presence and size of rotator cuff tears in each shoulder. The demographic factors that were analyzed included age, gender, side, and cuff thickness. All of these factors were evaluated with regard to their correlation with the presence of pain. Results: Of the 588 consecutive patients who met the inclusion criteria, 212 had an intact rotator cuff bilaterally, 199 had a unilateral rotator cuff tear (either partial or full thickness), and 177 had a bilateral tear (either partial or full thickness). The presence of rotator cuff disease was highly correlated with age. The average age was 48.7 years for patients with no rotator cuff tear, 58.7 years for those with a unilateral tear, and 67.8 years for those with a bilateral tear. Logistic regression analysis indicated a 50% likelihood of a bilateral tear after the age of sixty-six years (p < 0.01). In patients with a bilateral rotator cuff tear in whom one tear was symptomatic and the other tear was asymptomatic, the symptomatic tear was significantly larger (p < 0.01). The average size of a symptomatic tear was 30% greater than that of an asymptomatic tear. Overall, patients who presented with a full-thickness symptomatic tear had a 35.5% prevalence of a full-thickness tear on the contralateral side. Conclusions: There is a high correlation between the onset of rotator cuff tears (either partial or full thickness) and increasing age. Bilateral rotator cuff disease, either symptomatic or asymptomatic, is common in patients who present with unilateral symptomatic disease. As the size of a tear appears to be an important factor in the development of symptoms, we recommend surveillance at yearly intervals for patients with known rotator cuff tears that are treated nonoperatively.